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I.XH&, 


MANUAL 


OF 


SCIENCE  FOR  TEACHERS 


CONTAINING 

ANSWERS    TO    THE    PRACTICAL    QUESTIONS 

AND    PROBLEMS    IN    THE    AUTHOR'S 

SCIENTIFIC    TEXT-BOOKS 


BY 

j.  DORM: AN   STEE^E,  PH.D.,  K.  o.  s. 

AUTHOR    OF  THE   FOURTEEN-WEEKS   SERIES    IN    NATURAL   SCIENCE  ^^^ 

paftc 

Bi  < 

REVISED     EDITION 

TO   ACCOMPANY   THE   POPULAR    PHYSICS,    POPULAR    CHEMISTRY, 
PHYSIOLOGY,    AND    NEW    DESCRIPTIVE   ASTRONOMY 


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NEW  YORK  •:•  CINCINNATI  •:•  CHICAGO  >   r~* 

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AM:KRICAN   BOOK:  COMPANY 


A    POPULAR    SERIES 

IN 

NATURAL    SCIENCE, 


BY 


J.   DQR.MAN    STEELE,    F*n.D.,    K.O.S., 

A  uihor  of  the  Fourteen  Weeks  Series  in  Natural  Science,  etc.,  etc. 

New  Popular  Chemistry.  New  Descriptive  Astronomy. 

New  Popular  Physics.  New  Hygienic  Physiology. 

New  Popular  Zoology.  Popular  Geology. 

An  Introduction  to  Botany. 


The  Publishers  can  supply  (to  Teachers  only)  a  Manual  containing  Answers 
to  the  Questions  and  Problems  in  Steele's  entire  Series. 


BARNES'    HISTORICAL     SERIES, 

ON    THE    PLAN     OK 

STEELE'S    FOURTEEN-WEEKS     IN     THE     SCIENCES. 

A  Brief  History  of  the   United   States. 
A  Brief  History  of  France. 

A  Brief  History  of  Ancient  Peoples. 

A   Brief  History  of  Mediaeval   and    Modern    Peoples. 
A  Brief  General    History. 

A  Brief  History  of  Greece. 

A  Brief  History  of  Rome. 

A  Popular  History  of  the   United   States. 

Copyright,  1888,  by  A.  S.  BARNES  &  Co. 
J?<tuitiTr*w 

Add'l 


PREFACE. 


SINCE  the  publication  of  the  former  edition  of  this  Manual, 
Steele's  Physics  and  Chemistry  have  been  thoroughly  revised, 
and  the  Hygienic  Physiology  has  been  published.  The  present 
issue  has  been  prepared  to  accompany  these  later  editions,  and 
includes  complete  reference  to  all  the  problems  and  practical 
questions  contained  in  Steele's  Popular  Physics,  Popular  Chemis- 
try, Hygienic  Physiology,  and  New  Descriptive  Astronomy. 
Great  pains  have  been  taken  to  revise  and  compare  the  prob- 
lems, which  are  fully,  and,  it  is  thought,  accurately  solved. 
The  practical  questions,  as  in  the  former  edition  of  the  Manual, 
are  often  not  answered  in  full,  yet  sufficiently  so  to  furnish  a 
key  to  the  more  perfect  reply.  The  use  of  the  text-books  is 
presupposed,  and  the  statements  merely  supplement,  or  apply 
the  theories  therein  contained  and  explained.  Upon  many  points 
there  may  be,  and  often  is,  a  difference  of  opinion.  On  these 
mooted  questions  only  that  view  which  appeared  to  the  author 
to  have  preponderance  of  argument  has  been  advanced,  leaving 
the  subject  open  for  the  discussion  of  other  theories. 

The  former  edition  of  the  Manual  can  still  be  obtained  by 
those  teachers  who  continue  to  use  the  earlier  editions  of  the 
Sciences,  although,  with  a  few  exceptions,  the  problems  and 
questions  therein  answered  are  incorporated  with  those  which 
have  been  added  in  the  present  issue. 

DECEMBER,  1888. 

163 


ANSWERS    ;; 

TO    THE 

PKACTICAL  QUESTIONS  AND  PROBLEMS 

IN    THE 

POPULAR   PHYSICS. 

36 — !•  A  rifle-ball  thrown  against  a  board  standing 
on  its  end  will  knock  it  down  ;  the  same  bullet  fired  at  the 
board  will  pass  through  it  without  disturbing  its  position. 
Why  is  this? 

The  ball  which  is  thrown  has  time  to  impart  its  motion  to 
the  board;  the  one  fired  has  not. 

2.  Why  can  a  boy  skate  safely  over  a  piece  of  thin  ice, 
when9  if  he  should  pause,  it  would  break  under  him  di- 
rectly ? 

In  the  latter  case  there  is  time  for  the  weight  of  his  body 
to  be  communicated  to  the  ice;  in  the  former,  there  is  not. 

3.  WJiy    can  a   cannon-ball  be  fired  through  a  door 
standing  ajar,  without  moving  it  on  its  hinges  ? 

Because  the  cannon-ball  is  moving  so  quickly  that  its  mo- 
tion is  not  imparted  perceptibly  to  the  door. 

4.  Wliy  can  ^ve  drive  on  the  head  of  a  hammer  by  sim- 
ply striking  the  end  of  the  handle  ? 

This  can  only  be  done  by  a  quick,  sharp  blow,  which  will 
drive  the  wooden  handle  through  the  socket  before  the  motion 
has  time  to  overcome  the  inertia  of  the  iron  head.  A  slow, 
steady  blow  will  be  imparted  to  the  head,  and  so  fail  of  the 
desired  effect. 


2  AJVSWJSBS    TO    PRACTICAL     QUESTIONS 

5.  Suppose  you  were  on  a  train  of  cars  moving  at,  the 
rate  of  SO  miles  per  hour ;  ivith  ^vhat  force  ^vould  you  be 
thrown  forward  if  the  train  vvere  stopped  instantly  ? 

With  the  same  velocity  which  the  train  had,  or  44  feet  per 
second.  Your  momentum  would  be  your  mass  multiplied  by 
this  velocity. 

0.  In  what  line  does  a  stone  fall  from  the  mast-head  of 
a  vessel  in  motion  ? 

In  a  slightly  curved  line,  produced  by  the  two  forces — grav- 
ity and  the  forward  motion  of  the  vessel. 

7.  If  a  ball  be  dropped  from  a  high  tower  it  ivill  strike 
the  earth  a  little  east  of  a  vertical  line.     Why  is  this  ? 

In  the  daily  revolution  of  the  earth  on  its  axis,  from  west 
to  east,  the  top  of  the  tower  moves  faster  than  the  bottom,  be- 
cause it  passes  through  a  larger  circle.  "When,  therefore,  the 
ball  falls,  it  retains  that  swifter  easterly  motion,  and  so  strikes 
very  slightly  east  of  the  vertical. 

8.  It  is  stated  that  a  suit  was  once  brought  by  the  driver 
of  a  light  wagon  against  the  owner  of  a  coach  for  damages 
caused  by  a  collision.     The  complaint  was  that  the  latter 
was  driving  so  fast,  that  when  the  two  carriages  struck  the 
driver  of  the  former  was  throivn  forward  over  the  dash- 
board.   Show  how  his  own  testimony  proved  him  to  have 
been  at  fault. 

When  the  light  wagon  was  suddenly  stopped,  its  driver  went 
on  with  the  same  speed  at  which  the  wagon  was  moving.  That 
this  threw  him  forward  over  the  dash-board,  proves  his  speed 
to  have  been  unusual. 

9.  Suppose  a  train  moving  at  the  rate  of  3O  miles  per 
hour  ;  on  the  rear  platform  is  a  spring-gun  aimed  parallel 
'with  the  track,  and  in  a  direction  precisely  opposite'  to  the 
motion  of  the  car.    Let  a  ball  be  discharged  with  the  exact 
speed  of  the  train,  where  would  it  fall  ? 

In  a  vertical  line  to  the  track.  The  two  equal,  opposite  mo- 
tions would  exactly  destroy  each  other. 


IN    POPULAR    PHYSICS.  3 

10.  Suppose  a  steamer  in  rapid  motion  and  on  its  deck 
a  tnan  Jumping.     Can   he  jump  farther  by  leaping  the 
way  the  boat  is  moving  or  in  the  opposite  direction? 

It  will  make  no  difference  as  long  as  he  jumps  on  the  deck. 
Should  he  jump  off  the  boat,  then  the  effect  would  be  different. 

11.  Could  a  party  play  ball  on  the  deck,  of  an  ocean 
steam- ship  when  moving  along  at  the  rate  of   2O  miles 
per  hour,  without  making  allowance  for   the  motion  of 
the  ship  ? 

They  could.  The  ball  would  have  the  motion  of  the  ship, 
and  would  move  with  it  in  whatever  direction  they  might 
throw  it. 

37 — 12.  Since  "action  is  equal  to  reaction,"  why  is  it  not 
r,o  dangerous  to  receive  the  "kick"  of  a  gun  as  the  force 
of  the  bullet  ? 

The  kinetic  energy  varies  as  the  square  of  the  velocity ;  and 
the  velocity  with  which  the  gun  moves  backward  is  as  much 
less  than  that  with  which  the  bullet  moves  forward,  as  the  gun 
is  heavier  than  the  bullet.  For  this  reason  a  heavy  gun  will 
kick  much  less  than  a  light  one. 

13.  If  you  were  to  jump  from  a  carriage  in  rapid 
motion,  would  you  leap  directly  totvard  the  sx>ot  on  which 
you  wished  to  alight? 

No  ;  because  as  one  jumps  from  the  carriage  he  has  its  for- 
ward motion,  and  will  go  just  as  far  ahead,  while  leaping,  as 
he  would  if  he  had  remained  in  the  carriage.  He  should,  there- 
fore, aim  a  little  back  of  the  desired  alighting-place. 

14.  If  you  wished  to  shoot  a  bird  in  swift  flight,  would 
you  aim  directly  at  it? 

No.  The  bird  will  fly  forward  while  the  bullet  is  going  to 
it.  One  should,  therefore,  aim  a  little  in  advance. 

15.  At  ^vl^at  parts  of  the  earth  is  the  centrifugal  force 
the  least? 

The  poles.  The  distance  from  axis  to  surface  is  there  re- 
duced to  zero. 


4  ANSWERS     TO    PRACTICAL     QUESTIONS 

16.  What  causes  the  mud  to  fly  from  the  ivheels  of  a 
carriage  in  rapid  motion  ? 

The  centrifugal  force  (the  momentum  of  the  mud). 

1 7.  Wtiat  proof  have  ^ve  that  the  earth  was  once  a  soft 
tn  ass  ? 

It  is  flattened  at  the  poles.  This  effect  is  produced  upon  a 
ball  of  soft  clay  by  simply  revolving  it  on  a  wire  axis. 

18.  On  a  curve  in  a  railroad ,  ivhy  is  one  track  always 
higher  than  the  other  ? 

The  outer  track  is  raised  in  order  that  centrifugal  force  and 
gravity,  acting  together,  may  combine  to  keep  the  average 
pressure  perpendicular  to  the  track. 

19.  What  is  the  principle  of  the  sling  ? 

The  sling  is  whirled  until  a  strong  centrifugal  force  is  gen- 
erated ;  the  string,  the  centripetal  force,  is  then  released,  when 
the  stone  flies  off  at  a  tangent. 

20.  The  mouth  of  the  Mississippi  Miver  is  about  2\  miles 
farther  from  the  center  of  the  earth  than  its  source.     What 
causes  its  water  to  thus  "  run  up  hill "  ? 

The  centrifugal  force  produced  by  the  rotation  of  the  earth 
on  its  axis  tends  to  drive  the  water  from  the  poles  toward  the 
equator.  Were  the  earth  to  stand  still  in  its  daily  rotation,  the 
Gulf  of  Mexico  would  empty  its  waters  back  through  the  Mis- 
sissippi to  the  northern  regions. 

21.  Is  it  action  or  reaction  that  breaJcs  an  egg  ivheti  1 
striJte  it  against  the  table  ? 

The  reaction  of  the  table. 

22.  Was  the  tnan  philosophical  who  said  "  it  tvas  not 
the  falling  so  far   but   the   stopping  so  quick  that  hurt 
him"? 

He  was. 

23.  If  one  person  rims  against  another,  which  receives 
the  greater  bloiv  ? 

Action  is  equal  to  reaction  ;  hence  the  momentum  given  up 
by  the  one  is  equal  to  that  received  by  the  other. 


IN    POPULAR    PHYSICS.  5 

24.  Would  it  vary  the  effect  if  the  two  persons  were 
running  in  opposite  directions  ? 

The  blow  would  then  be  the  sum  of  both  their  momenta. 

If  they  were  running  in  the  same  direction  ? 

The  blow  would  be  equal  to  the  difference  of  their  momenta. 

25.  Why  can  you  not  fire  a  rifle-ball  around  a  hill? 

Because  a  single  force  always  produces  motion  in  a  straight 
line. 

26.  Wliy  does  a  heavy  gun  "kick"  less  than  a  light 
one  ? 

See  problem  12. 

27.  A  man  on  the  deck  of  a  large  steamer  draws  a 
stnall  boat  toward  him.     Can  yott  express  the  ratio  of  the 
ship's  motion  to  that  of  the  boat  ? 

The  ship  moves  as  much  less  distance  than  the  boat,  as  the 
boat's  mass  is  less  than  that  of  the  ship. 

28.  Suppose  a  string,  fastened  with  a  nail  at  one  end, 
will  just  support  a  weight  of  25  Ibs.  at  the  other.    Unfasten 
it,  and  let  tivo  persons  piill  upon  it  in  opposite  directions. 
How  much  can  each  pull  ivithout  breaking  it  ? 

25  Ibs.  The  second  person,  in  the  latter  case,  can  pull  as 
much  as  the  nail  did  in  the  former.  The  tension  in  the  string 
is  25  Ibs.,  and  the  action  of  the  one  person  is  just  balanced  by 
the  reaction  of  the  other. 

29.  Can  a  man   standing  on   a  plat  form- scale  make 
himself  lighter  by  lifting  up  on  himself? 

He  can  not ;  because  action  and  reaction  are  equal  and  op- 
posite. 

30.  Why  can  not  a  man  lift  himself  by  pulling  up 
on  his  boot-straps  ? 

See  last  problem. 

31.  With  ivhat  momentum  would  a  steam-boat  weigh' 
ing  1,OOO  tons,  and  moving  with  a  velocity  of  1O  feet  per 
second,  strike  against  a  sunken  rock  ? 


6  ANSWERS    TO    PRACTICAL     QUESTIONS 

•  1,000  tons  =  2,000,000  Ibs.    2,000,000  x  10  =  20,000,000  units 
of  momentum. 

32.  With  what  momentum  would  a  train  of  cars  weigh- 
ing 1OO  tons,  and  running  1O  miles  per  hour,  strike  against 
an  obstacle  ? 

The  velocity  per  second  is  14f  feet.  100  tons  =  200,000  Ibs. 
The  momentum  is  200,000  x  14f  =  2,933, 333^  units  of  momen- 
tum. 

33.  Wliat  would  be  the  comparative  kinetic  energy  of' 
two  hammers,  one  driven  with  a  velocity  of  2Q  feet  per 
second,  and  the  other  1O  feet  ? 

202  =  400.     102  =  100.     400  :  100  : :  4  :  1. 

Hence  the  kinetic  energy  of  the  first,  or  its  ability  to  ac- 
complish work,  will  be  four  times  that  of  the  second.  This 
principle  is  of  great  importance  in  all  cases  where  percussion  is 
concerned.  The  highest  velocity  attainable  is  to  be  sought. 

34.  If  a  1OO  horse-poiver  engine  can  propel  a  steamer 
5  miles  per  hour,  ivill  one  of  20O  Jiorse-poivcr  double  its 
speed  ? 

By  no  means.  Resistance  is  proportional  to  /y2.  (See  Popu- 
lar Physics,  p.  65.)  To  double  the  velocity  would  require  over 
400  horse-power. 

3<>.  Why  are  ships  becalmed  at  sea  sometimes  floated 
toy  strong  currents  into  dangerous  localities  without  the 
Knowledge  of  the  crew  ? 

As  there  are  no  fixed  objects  with  which  to  compare  their 
motion,  the  officers  are  not  sensible  of  any  movement,  and  so 
are  drifted  far  out  of  their  course. 

38—56*.  A  man  in  a  ^vagon  holds  a  50-lb.  weight  in  his 
hand.  Suddenly  the  wagon  falls  over  a  precipice.  Will 
he,  while  dropping,  bear  the  strain  of  the  ^veight  ? 

No.  While  on  solid  ground,  his  hand  resisted  the  tendency 
of  the  weight  to  fall  toward  the  earth's  center  of  gravity  ;  but 
all  are  now  descending  freely  under  the  influence  of  gravity, 
and  he  no  longer  feels  the  pressure. 


IN    POPULAR    PHYSICS.  7 

37.  Wliy  are  we  not  sensible  of  the  rapid  motion  of  the 
earth  ? 

Because  all  the  objects  around  us  are  moving  in  the  same 
direction  with  the  earth,  and  there  is  nothing  at  hand  with 
which  to  compare. 

38.  A  feather  is  dropped  from  a  balloon  which  is  im- 
mersed in  and  swept  along  by  a  swift  current  of  air.     Will 
the  feather  be  blown  away,  or  will  it  appear  to  a  person  in 
the  balloon  to  drop  directly  doivu  ? 

It  will  seem  to  drop  directly  downward,  as  if  in  a  dead 
calm.  Its  fall  is  vertical,  however,  only  as  regards  the  balloon, 
and  not  as  regards  the  earth. 

(See  Stewart's  Physics,  p.  18.) 

39.  Suppose  a  bomb-shell,  flying  through  the  air  at  the 
rate  of  5OO  feet  per  second,  explodes  into  two  parts  of  equal 
weight,  driving  one  half  forward  in  the  same  direction  as 
before,  but  with  double  its  former  velocity.     What  would 
become  of  the  other  half? 

One  half  will  go  forward  with  a  double  velocity  (—  1,000  feet 
per  sec.),  and  the  other  half  will  be  checked  and  will  fall  directly 

to  the  ground. 

(See  Stewart's  Physics,  p.  37.) 

40.  Wliich  ivould  have  the  greater  penetrating  power, 
a  small  cannon-ball  with  a  high  velocity,  or  a  large  one 
with  a  low  velocity  ? 

The  former  would  penetrate,  while  the  latter  would  have 
the  greater  momentum.  .  - 

41.  There  is  a  story  told  of  a  man  who  erected  a  huge 
pair  of  bellows  in  the  stern  of  his  pleasiire-boat9  that  lie 
miglit  always  have  a  fair  ^vind.     On  trial,  the  plan  failed. 
In  which  direction  should  he  have  turned  the  belloivs  ? 

In  the  manner  adopted  at  first,  of  turning  the  nozzle  toward 
the  sails,  the  action  of  the  wind  against  the  sails  and  the  reac- 
tion of  the  bellows  against  the  boat  just  balanced  each  other. 
If  the  man  had  turned  the  nozzle  backward,  he  could  have  saved 
the  reaction  of  the  bellows  to  move  the  boat.  This  would,  how- 
ever, have  been  a  costly  and  bungling  mode  of  navigation. 


8  ANSWERS    TO    PRACTICAL,     QUESTIONS 

42.  If  a  man  and  a  boy  were  riding  in  a  wagon,  and, 
on  coming  to  the  foot  of  a  hill,  the  man  should  take  up  the 
boy  in  his  arms,  ^vould  that  help  the  horse  ? 

No  change  would  be  produced  in  the  weight  of  the  entire 
establishment  drawn  by  the  horse,  as  no  readjustment  of  the 
load  would  modify  the  attraction  of  gravity  which  produces  the 
weight.  Also,  action  —  reaction  ;  so  the  man  would  press  down 
on  the  wagon  an  amount  equal  to  the  weight  of  the  boy. 

4:3.  If  we  ivliirl  a  pail  of  tvater  swiftly  around  on  its 
oivn  axis,  ivhy  will  the  water  tend  to  leave  the  center  of 
the  pail  ? 

The  centrifugal  force  is  compounded  with  the  force  of  grav- 
ity, and  at  each  point  of  the  surface  the  water  level  is  at  right 
angles  to  their  resultant.  The  centrifugal  force  increases  with 
distance  from  the  axis,  hence  the  water  surface  becomes  con- 
cave. 

44.  IVJiy  will  the  foam  collect  at  the  holloiv  in  the  cen- 
ter? 

The  foam,  being  lighter  than  the  water,  has  less  momen- 
tum, in  proportion  to  its  volume,  and  is  forced  back  by  the 
heavier  particles. 

45.  If  tivo  cannon-balls,  one  weighing  8  Ibs.  and  the 
other  2  Ibs.,  be  /ired  ^vith  the  same  velocity,  which  will  go 
the  farther  ? 

The  former  has  much  less  surface  in  proportion  to  its  weight. 
It  will  therefore  go  much  farther  against  the  resistance  of  the 
air. 

46.  Resolve  the  force  of  the  wind  tvhich  turns  a  com- 
mon ivindmill,  and  show  hoiv  one  part  acts  to  push  the 
tvJieel  against  its  support,  and  one  to  turn  it  around. 

This  case  is  exactly  like  that  of  the  action  of  the  wind 
against  the  sail  of  a  ship,  as  shown  in  the  text  on  p.  29. 

47.  When  an  animal  is  jumping  or  falling,  can  any 
exertion  made  in  mid-air  change  the  motion  of  its  center 
of  gravity  ? 


AV    POPULAR    PHYSICS.  9 

The  center  of  gravity  falls  steadily  16.08  feet,  whatever 
other  force  may  act  on  the  body. 

(See  Second  Law  of  Motion.) 

48.  If  one  is  riding  rapidly,  in  which  direction  will  he 
be  thrown  when  the  horse  is  suddenly  stopped  ? 

In  the  same  direction  in  which  he  is  going.  He  has  the 
motion  of  the  carriage,  and  his  momentum  carries  him  for- 
ward. 

49.  When  standing  in  a  boat,  why,  as  it  starts,  are  we 
thrown  backivard  ? 

Because  our  bodies  tend  to  remain  stationary,  while  the 
boat  carries  our  feet  forward. 

50.  When  carrying  a  cup  of  tea,  if  we  move  or  stop 
quickly,  why  is  the  liquid  liable  to  spill  ? 

The  momentum  of  the  tea  tends  to  keep  it  still  or  in  mo- 
tion, as  the  case  may  be.  If  we  move  the  cup  quickly,  the 
motion  is  not  imparted  to  the  liquid  soon  enough  to  overcome 
this  momentum.  "When,  therefore,  we  start,  the  tea  spills  out 
backward ;  or,  when  we  stop,  it  spills  out  forward.  We  under- 
stand this  if  we  can  tell  why  a  cup  of  tea  is  more  liable  to 
spill  than  one  of  sugar. 

51.  Why,  when  closely  pursued,  can  we  escape  by  dodg- 
ing? 

"We  turn  sharply.  Our  pursuer,  ignorant  of  our  design,  can 
not  overcome  his  momentum  so  as  to  turn  as  quickly,  and 
hence  is  carried  past. 

52.  WJiy  is  a  carriage  or  sleigh,  'when  sharply  turning 
a  corner,  liable  to  tip  over  ? 

Because  its, momentum  tends  to  carry  it  directly  forward. 

53.  Wiiy,  if  you  place  a  card  on  your  finger,  and  on  top 
of  it  a  cent,  can  you  snap  the  card  from  under  the  cent 
without  knocking  tJie  latter  off  your  finger  ? 

Because  the  friction  between  the  card  and  the  cent  is  so 
slight  that,  by  a  quick  snap,  you  can  give  motion  to  the  former 
without  affecting  the  latter  enough  to  make  it  fall  off. 


10  AJSWJBRS    TO    PRACTICAL     QUESTIONS 

54.  Why  is  a  "  running  jump  "  longer  than  a  "  stand- 
ing jump  "  ? 

This  is  an  example  under  the  first  law  of  motion.  The  mo- 
mentum of  the  person  when  running  (mxv)  is  added  to  the 
force  with  which  he  finally  springs  from  the  ground  for  the 
jump. 

55.  Why,  after  the  sails  of  a  vessel  are  furled,  does  it 
still  continue  to  move  ?  and  why,  after  the  sails  are  spread, 
does  it  require  some  tiine  to  get  it  under  full  headway? 

This  illustrates  the  tendency  of  matter  to  continue  in  its 
present  state,  whether  of  rest  or  of  moticn.  For  the  former 
part  of  the  question,  apply  the  first  law  of  motion,  and  for  the 
latter,  the  second  paragraph  on  p.  21  cf  the  Physics.  If,  on 
starting  with  a  heavy  load,  the  horses  leap  suddenly  forward, 
they  will  break  the  harness ;  but,  by  a  steady,  constantly-in- 
creased draught,  they  will  communicate  motion  to  the  mass. 

56.  Why  can  a  tallow  candle  be  fired  through  a  board? 

Because  of  its  high  velocity.  Motion  can  not  be  communi- 
cated at  once  to  the  entire  mass  of  the  board,  hence  this  yields 
at  the  place  where  pressure  is  suddenly  applied. 

COHESION. 

48 — !•  Why  can  we  not  weld  apiece  of  copper  to  one  of 
iron  ? 

Cohesion  acts  most  readily  between  molecules  of  the  same 
kind. 

2.  Why  is  a  bar  of  iron  stronger  than  one  of  wood  ? 

All  we  can  say  is  that  there  is  more  cohesion  between  its 
molecules.  The  wood,  moreover,  is  perforated  with  minute  hol- 
low tubes,  so  that  its  molecules  can  not  be  so  compactly  massed 
together  as  those  of  the  iron. 

3.  Why  may  a  piece  of  iron,  when  perfectly  ivelded,  be 
stronger  than  before  it  was  broken  ? 

By  the  hammering,  more  particles  are  brought  within  the 
range  of  cohesion. 


IN    POPULAR    PHYSICS.  11 

4.  Why  do  drops  of  different  liquids  vary  in  size  ? 

Because  they  vary  in  cohesive  force. 

5.  Why,  when   you  drop  medicine,  will  the  last  few 
drops  contained  in  the  bottle  be  of  a  larger  size  than  the 
others  ? 

The  pressure  of  the  liquid  in  the  bottle  is  less,  and  there- 
fore they  form  more  slowly. 

6.  Why  are  drops  larger  if  you  drop  them  sloivly? 

There  is  more  time  for  the  adhesive  force  of  the  bottle  to 
act  on  the  liquid,  and  so  a  larger  drop  can  be  gathered. 

7.  Why,  if  you  melt  scraps  of  zinc,  will  they  form  a 
solid  mass  w/ien  cooled  ? 

The  heat  overcomes,  in  part,  the  attraction  of  cohesion,  so 
that  the  particles  flow  freely  on  each  other.  They  now  all 
come  within  the  range  of  cohesion,  so  that  when  the  metal 
cools  they  are  held  by  that  force  in  a  solid  mass. 

8.  In  what  liquids  is  the  force  of  cohesion  greatest? 

Mercury,  molasses,  etc. 

9.  Name  some  solids  that  will  volatilize  tvithout  melt- 
iny. 

Arsenic,  camphor. 

10.  Why  can  glass  be  ivelded  ? 

Because,  like  iron,  it  becomes  viscous  before  melting. 

11.  Name  some  substances  that  can  not  be  ivelded.    Why 
not? 

Wood  can  not  be  welded,  nor  can  lead  or  bismuth.  They 
can  not  be  made  to  assume  the  viscous  condition. 

12.  What  liquids  would  you  select  for  showing  surface 
tension  ? 

Solution  of  soap  in  water  is  the  most  convenient.  The  dif- 
ference in  tension  between  films  of  different  kinds  of  liquid  is 
well  shown  by  carefully  dropping  oil  of  coriander  or  oil  of  cin- 
namon, or  minute  fragments  of  clean  camphor  on  the  surface 
of  perfectly  clean  water. 


12  ANSWERS    TO    PRACTICAL     QUESTIONS 

ADHESION. 

54 — 1.  Why  does  cloth  shrink  when  wet  ? 

By  adhesion  the  water  is  drawn  into  the  pores  of  the  cloth. 
The  fibers  are  thus  expanded  sidewise  and  shortened  length- 
wise. The  cloth  "fulls  up"  or  thickens  while  it  shortens  and 
narrows  (shrinks)  in  the  process. 

2.  Why  do  sailors  at  a  boat-race  wet  the  sails  ? 

The  pores  being  full  and  expanded  make  the  sails  more 
compact.  They  will,  therefore,  hold  the  wind  better. 

3.  WJiy  does  not  writing-paper  blot  ? 

Because  the  pores  are  filled  with  sizing.  (See  Popular  Chem- 
istry, p.  216.) 

4.  IVJiy  does  paint  tend  to  prevent  wood  from  shrink- 
ing? 

Because  it  fills  the  pores  of  the  wood  at  its  surface. 

5.  What  is  the  shape  of  the  surface  of  a  glass  of  water 
and  one  of  mercury? 

Ordinarily  the  former  is  concave  and  the  latter  convex. 

6.  Why  can  ^ve  not  dry  a  toivel  perfectly  by  wringing  ? 

Because  of  the  strength  of  the  force  of  adhesion,  by  which 
the  water  is  held  in  the  pores  of  the  cloth. 

7.  Why  will  not  water  run  through  a  fine  sieve  when 
the  wires  have  been  greased  ? 

Because  of  reversed  capillarity  between  oil  and  water. 

8.  Why  will  camphor  dissolve  easily  in  alcohol  and  not 
in  water  ? 

Because  there  is  a  strong  adhesion  between  the-  alcohol  and 
camphor,  and  but  little  between  the  water  and  camphor. 

,9.  Why  tvill  mercury  rise  in  zinc  tubes  as  ivater  does  in 
glass  tubes  ? 

Because  of  the  strong  adhesion  between  zinc  and  mercury. 


IN   POPULAR    PHYSICS.  13 

10.  Why  will  ink  spilled  on  the  edge  of  a  booh  extend 
farther  inside  than  if  spilled  on  the  side  of  the  leaves? 

Because  the  sensible  pores  of  the  paper  are  short,  being  only 
the  thickness  of  a  leaf,  while  the  spaces  between  the  leaves  are 
longer  and  continuous. 

11.  If  you  should  happen  to  spill  some  ink  on  the  edge 
of  your  book,  ought  you  to  press  the  leaves  together  ? 

Yes ;  to  make  it  as  nearly  solid  as  possible,  until  blotting  pa- 
per can  be  applied  to  remove  what  has  not  soaked  into  the  book. 

12.  Wliy  can  yon  not  mix  oil  and  water  ? 

Because  there  is  little  adhesion  between  them. 

13.  IVliy  ^vill  water  wet  your  hand  while  mercury  will 
not? 

Because  in  the  former  case  there  is  strong  adhesion,  in  the 
latter  but  little. 

14.  Why  is  a  tub  or  pail  liable  to  fall  to  pieces  if  not 
filled  tvith  water  or  kept  in  the  cellar  ? 

Because  the  moisture  dries  out  of  the  pores,  and  the  wood 
shrinks  so  as  to  let  the  hoops  fall  off. 

15.  Name  instances  where  the  attraction  of  adhesion  is 
stronger  than  that  of  cohesion. 

"Wood  fastened  by  glue  will  often  split  before  the  glue  will 
yield.  Paper  stuck  with  paste,  and  bricks  with  mortar,  are  also 
examples. 

16.  Wliy  does  the  ivater  in  Fig.  18  stand  higher  inside 
of  the  tube  than  next  the  glass  on  the  outside  ? 

There  is  the  influence  of  a  larger  surface  of  glass  in  pro- 
portion to  the  quantity  of  water  to  be  lifted. 

17.  Why  will  clothes-lines  tighten  and  sometimes  break 
during  a  shower  ? 

The    rope   absorbs   water,   and    expands   transversely.  This 

shortens    it    with  so  much    force    as    often    to    break    it.  The 

shrinking   of    new  cloth  when  wet  illustrates   the  same  prin- 
ciple. 


14  ANSWERS    TO    PRACTICAL     QUESTIONS 

IS.  In  casting  large  cannon,  the  gun  is  cooled  by  a 
stream  of  cold  water.  Why  ? 

The  object  of  this  is  to  cause  the  iron  to  cool  more  quickly, 
and  so  not  give  the  molecules  time  to  arrange  themselves  in 
crystals. 

19.  Why  does  paint  adhere  to   wood?      Chalk  to  the 
blackboard  ? 

These  are  illustrations  of  the  force  of  adhesion. 

20.  Wliy  does  a  toivel  dry  one's  face  after  washing  ? 

The  sensible  pores  of  the  cloth  absorb  the  water  from  the 
face  by  adhesion. 

21.  Why  will  a  greased  needle  float  on  water  ? 

The  grease  prevents  the  needle  from  being  wetted,  and  the 
toughness  of  the  surface  film  cf  water  is  sufficient  to  with- 
stand the  weight  of  the  needle. 

22.  IVhy  is  the  point  of  a  pen  slit  ? 

So  that  we  may  widen  at  will  the  surface  of  contact  be- 
tween the  ink  and  the  paper.  The  ink  is  prevented  from  de- 
scending rapidly,  when  the  slit  is  not  open,  by  the  grip  of  its 
surface  film. 

23.  Why  is  a  thin  layer  of  glue  stronger  than  a  thick 
one  ? 

The  adhesion  between  the  glue  and  the  wood  is  stronger 
than  the  cohesion  between  the  particles  of  glue ;  hence  the 
thinner  the  layer  of  glue  the  fewer  the  particles  acted  upon 
only  by  the  latter  or  weaker  force. 


GRAVITATION. 

73 — !•  JVlien  an  apple  falls  to  the  ground,  hoiv  much 
does  the  earth  rise  to  meet  it  ? 

The  earth  falls  as  much  less  distance  than  the  apple,  as  its 
mass  is  greater. 


IN   POPULAR    PHYSICS.  15 

2.  Will  a  body  weigh  more  in  a  valley  than  on  a  mount- 


It  will,  because  the  distance  to  the  earth's  center  is  less, 

.7.  Will  a  pound  weight  fall  more  slowly  than  a  two- 
pound  weight  ? 

They  will  both  fall  in  the  same  time,  except  the  slight  dif-  ^ 
ference  which  is  caused  by  the  resistance  of  the  air.  Galileo  (^ 
propounded  this  view,  and  proved  it,  in  the  presence  of 
nesses,  by  letting  unequal  weights  fall  from  the  leaning  tower 
of  Pisa. 

4.  How  deep  is  a  well9  if  it  takes  three  seconds  for  a  stone 
to  fall  to  the  bottom  of  it  ? 

S-igt2 

S  =  16  x  3-  =  144  feet. 

5.  Is  the  center  of  gravity  always  ivithin  a  body  —  as, 
for  example,  a  pair  of  tongs  ? 

No.  It  may  be  entirely  outside,  and  is  usually  so  for  a  pair 
of  tongs. 

6.  In  a  ball  of  equal  density  throughout,  ivhere  is  the 
center  of  gravity  ? 

At  the  center  of  the  ball. 

7.  Why  does  a  ball  roll  down  hill  ? 

Because  the  line  of  direction  falls  without  the  small  base  of 
the  ball. 

S.  Why  is  it  easier  to  roll  a  round  body  than  a  square 
one? 

Because  the  base  of  the  ball  is  so  much  smaller,  and  there- 
fore the  center  of  gravity  need  not  be  raised  to  bring  the  line 
of  direction  without. 

9.  Why  is  it  easier  to  tip  over  a  load  of  hay  than  one  of 
stone  ? 

Because  the  center  of  gravity  in  a  load  of  hay  is  very  high, 
and  in  a  load  of  stone  very  low.  Therefore  the  center  of  grav- 


16  ANSWERS    TO    PRACTICAL     QUESTIONS 

ity  in  the  former  need  not  be  raised  much  to  bring  the  line  of 
direction  without  the  base,  while  in  the  latter  it  must  be. 

1 0.  Why  is  a  pyramid  the  stablest  of  structures  ? 

Because  the  base  is  so  broad  and  the  center  of  gravity  so 
low.  The  center  of  gravity  must  therefore  be  lifted  very  high 
before  the  line  of  direction  will  fall  without  the  base. 

11.  When  a  hammer  is  thrown,  on  which  end  does  it 
most  often  strike  ? 

The  heavier  end. 

12.  Why  does  a  rope-ivalker  carry  a  heavy  balancing- 
pole? 

Because  in  this  way  he  can  easily  shift  his  center  of 
gravity. 

13.  Wliat  would  become  of  a  ball  if  dropped  into  a  hole 
bored  through  the  center  of  the  earth  ? 

If  we  assume  the  earth  to  be  at  rest,  the  ball  will  move 
with  diminishing  acceleration,  but  increasing  speed,  to  the  cen- 
ter. The  momentum  thus  acquired  would  carry  it  an  equal 
distance  beyond,  if  there  be  no  resistances,  and  the  acceleration 
being  now  negative,  the  ball  will  be  brought  momentarily  to 
rest  at  the  surface  on  the  opposite  side.  It  will  then  fall  back 
past  the  center,  and  continue  thus  oscillating  forever.  If  we 
assume  the  earth  to  be  rotating,  the  ball  will  sink  from  fast- 
moving  toward  slow-moving  parts,  and  strike  against  the  side 
of  the  hole.  Friction  will  soon  bring  it  to  rest  at  the  earth's 
center. 

1£.  Would  a  clock  lose  or  gain  time  if  carried  to  the  top 
of  a  mountain  ? 

i  It  would  lose  time,  because  the  force  of  gravity  would  be 
lessened.  At  the  North  Pole  it  would  gain  time,  because  there 
the  force  of  gravity  would  be  increased. 

15.  In  the  winter,  would  you  raise  or  lower  the  pendu- 
lum-bob  of  your  clock? 


IiV    POPULAR    PHYSICS.  17 

I  would  lower  it,  since  the  cold  of  winter  shortens  the  pen- 
dulum, and  this  movement  of  the  bob  would  counteract  that 
change. 

16.  IVliy  is  the  pendulum-bob  generally  made  flat  ? 

To  decrease  the  friction  of  the  air. 

It  '.  IVJiat  beats  off  the  time  in  a  ivatch  ? 

The  vibration  of  the  balance-wheel. 

IS.  Is  solved  in  the  book. 

19.  What  should  be  the  length  of  a  pendulum  at  New 
York  to  vibrate  half-seconds  ? 

(1  sec.)2  :  (~|-  sec.)2  ::  39.1  in.  :  x  —  9.  7  +  inches. 

To  vibrate  quarter-seconds  ? 

(1  sec.)2  :  (£  sec.)2  ::  39.1  in.  :  x  =  2.  4  +  inches. 
To  vibrate  hours  ? 

(1  sec.)2  :  (3600  sec.)2  :  :  39.1  in.  :  x  =  7997.7  miles.* 

20.  What  is  the  proportionate  time  of  vibration  of  two 
pendulums,  16  and  64  inches  long,  respectively  ? 

According  to  the  2d  law  of  pendulums, 
Time  of  vib.  of  1st  :  Time  of  vib.  of  2d  :  :     /16  :  *Qi  :  :  4  :  8  :  :  1  :  2. 


21.  Why,  when  you  are  standing  erect  against  a  ivall, 
and  a  piece  of  money  is  placed  between  your  feet,  can  you 
not  stoop  fonvard  and  pick  it  up  ? 

By  leaning  forward  you  bring  the  center  of  gravity  in  front 
of  your  feet,  and,  as  on  account  of  the  wall,  you  can  not 
throw  any  part  of  your  body  back  to  preserve  the  balance,  you 
fall  forward. 

22.  If  a  toiver  ivere  198  feet  high,  with  tvhat  velocity 
ivould  a  stone,     dropped   from   the   summit,   strike   the 
ground  ? 

&  =  2gh    (See  p.  64,  foot-note.) 
v*  =  64x198 
v  =  112.5  feet. 

*  Nearly  the  diameter  of  the  earth. 


18  ANSWERS    TO    PRACTICAL     QUESTIONS 

23.  A  body  falls  in  5  seconds:   with  what  velocity  does 
it  strike  the  ground  ? 

v  =  32t.     v  =  32x5.     v  =  160  feet. 

74  —  24.  Hoiv  far  ivill  a  body  fall  in  1O  seconds? 

s  =  16£2.    s  =  16  x  102  =  1600  feet. 
With  what  velocity  ivill  it  strike  the  ground  ? 

v  =  32t.    v  =  32  x  10  =  320  feet. 

25.  A  body  is  thrown  upward  with  a  velocity  of  11)2 
feet  the  first  second  ;  to  what  lieight  will  it  rise  ? 

Equation  (1),  v  =  32t.     192  =  32t.     t  =  Q  sec. 
(2),  s  =  16£2.     s  =  16  x  62  =  576  feet. 

26.  A  ball  is  shot  upward  with  a  velocity  of  250  feet  ; 
to  what  height  ivill  it  rise?    How  long  ivill  it  continue  to 
ascend  ? 

Using  equations  (1)  and  (2),  as  in  the  last  problem,  we  have 

t  =  8  sec. 
s  =  1024  feet. 

28.  Are  any  two  plumb-lines  parallel  ? 

They  are  not,  since  they  point  to  the  earth's  center  of  grav- 
ity.   No  two  spokes  of  a  wheel  can  be  parallel. 

29.  A  stone  let  fall  from  a  bridge  strikes  the  water  in 
three  seconds.     What  is  the  lieight  ? 


s  =  16£2.     s  -  16  x  32  =  144  feet. 

30.  A  stone  falls  from  a  church  steeple  in  4:  seconds. 
Wfiat  is  the  height  ? 

s  =  16P.     s  =  16  x  42  =  256  feet. 

31.  How  far  would  a  body  fall  the  first  second  at  a 
height  of  12,OOO  miles  above  the  earth's  surface? 

(16,000  mi.)2  :  (4000  mi.)2  :  :  16  feet  :x  =  l  foot. 

32.  A  body  at  the  surface  of  the  earth  weighs  WO  tons; 
what  would  be  its  weight  1,OOO  miles  above  ? 

(5000  mi.)2  :  (4000  mi.)2  :  :  100  tons  :  x  -  64  tons. 


I2V   POPULAR    PHYSICS.  19 

33.  A  boy  ivishing  to  find  the  height  of  a  steeple  lets  flu 
tin  arrow  that  just  reaches  the  top,  and  then  falls  to  the 
ground.  Tt  is  in  the  air  6  seconds.  Required  the  height. 

s  =  16t*.    s  =  16  x  32  =  144  feet. 

34.  An  object  let  fall  from  a  balloon  reaches  the 
ground  in  1O  seconds.  Required  the  distance. 

s  =  16  x  108  =  1600  ft. 

35.  In  what  time  will  a  pendulum  4O  feet  long  make  a 
vibration  ? 

According  to  the  2d  law  of  pendulums,  and  taking  the 
length  of  a  seconds  pendulum  as  39  in.,  we  have: 


1  sec.  :  x  : :  y^39  =^40  x  12  in. 

'480 
39 
x  =  3. 5  + sec. 

36.  Two  bodies  in  space  are  12  miles  apart.      They 
weigh   1OO  and  2OO   Ibs.   respectively.     If   they   should 
fall  together  by  force   of  their  mutual  attraction,  what 
portion  of  the   distance   would   be  passed   over  by  each 
body  ? 

The  distance  passed  over  by  the  two  bodies  is  inversely  as 
their  mass  ;  hence  one  moves  8  miles  and  the  other  4  miles. 

37.  If  a  body  weighs  2,OOO  Ibs.  upon  the  surface  of 
the  earth,  what  would  it  weigh  2,OOO  miles  above  ? 

(6000  mi.)2 :  (4000  mi.)2 :  :  2000  Ibs.  :  x  =  888f  Ibs. 
Hoiv  much  5OO  miles  above  ? 

(4500  mi.)2 :  (4000  mi.)2 : :  2000  Ibs.  :  x  =  1580  + Ibs. 

38.  At  what  distance  above  the  surface  of  the  earth  will 
a  body  fall,  the  first  second,  21\  inches? 

A  body  falls  16  feet*  (192  inches)  at  the  surface  of  the 
earth.  21^  inches  are  \  of  192  inches.  Now,  as  the  attraction 
is  inversely  as  the  square  of  the  distance,  the  distance  must  be 

*  According  to  the  best  authorities  the  distance  is  more  nearly  16^$  feet. 


20  ANSWERS    TO    PRACTICAL     QUESTIONS 

/y/9,  or  3  times  that  at  the  surface.  Hence,  the  body  must  be 
12,000  miles  from  the  center,  or  8,000  miles  from  the  surface 
of  the  earth.  The  problem  may  be  solved  directly  by  propor- 
tion, thus  : 

x*  :  40002  :  :  192  inches  :  21|  inches. 

x  =  12000  miles  (distance  from  the  center). 

12000  miles—  4000  miles  =  8000  miles. 

89.  How  far  will  a  body  fall  in  8  seconds  ?  1,O24  feet. 
—  In  the  8th  second?  24O  feet.—  In  1O  seconds?  1,6OO 
feet.—  In  the  3Oth  second  ?  944  feet. 

4O.  Hoiv  long  would  it  take  for  a  pendulum  one  mile  in 
length  to  make  a  vibration  ? 

According  to  the"1  second  law  of  pendulums  (Physics,  p.  69), 


1  sec.  :  x  :  :^S9  :A/5280x  12  in. 
x  =  40  +  sec. 

41.  Wliat  would  be  the  time  of  vibration  of  a  pendulum 
04  meters  long  ? 

(1  sec.)2  :  y?  :  :  1  meter  (nearly)  :  64  meters. 
x  =  8  seconds  (nearly). 

42.  A  ball  is  dropped  from  a  height  of  64  feet.    At  the 
same  moment  a  second  ball  is  thrown  upward  with  suffi- 
cient velocity  to  reach  the  same  point.     Where  will  the  two 
balls  pass  each  other  ? 

At  the  end  of  one  second.  The  first  ball  would  fall  64  feet 
in  2  seconds  ;  the  second  would  rise  for  2  seconds,  and  they 
would  pass  in  1  second,  48  feet  above  the  ground. 

43.  Explain  the  following  fact  :  A  straight  stick  loaded 
with  lead  at  one  end  can  be  more  easily  balanced  vertically 
on  the  finger  when  the  loaded  end  is  upivard  than  when 
it  is  doivnward. 

When  the  loaded  end  is  upward  a  slighter  motion  is  needed 
to  bring  the  line  of  direction  within  the  base.  The  principle  is 
similar  to  that  of  the  balancing-pole  of  the  gymnast. 


IN    POPULAR    PHYSICS.  21 

44.  If  a  body  weighing  1  Ib.  on  the  earth  were  carried 
to  the  sun,  it  would  weigh  27  Ibs.  How  much  would  it  at- 
tract the  sun  ?  Ans.  27  Ibs. 

75 — 45.   Why  does  watery  vapor  float  and  rain  fall  ? 

Perfect  vapor,  which  is  quite  invisible,  is  lighter  than  air, 
and  is  diffused  through  it.  When  condensed  into  minute  drop- 
lets forming  clouds,  these  are  prevented  from  falling  fast  be- 
cause of  the  great  amount  of  surface,  in  proportion  to  their 
weight,  exposed  to  the  resistance  of  the  air. 

46.  If  a  body  weighs  1O  Jcilos.  on  the  surface  of  the 
earth,  ^v1lat  ivill  it  ^veigh  1,OOO  km.  above  ? 

x  :  10  kilos.  : :  (6,366  *)2 :  (7.36G)2 
x  =  7.5  kilograms. 

47.  A  body  is  thrown  vertically  upward  with  a  velocity 
of  1OO  meters.    Hoiv  long  before  it  ivill  return  to  its  origi- 
nal position  ?    Ans.  2O.4  seconds. 

48.  How  much  time  will  be  required  for  a  body  to  fall 
a  distance  of  2,OOO  meters  ? 

Equation  (6)     s  =  $gl*.     2,000  =  ?LpP. 
.-.  t  =  20.2  seconds. 

49.  IVJiat  would  be  the  time  of  vibration  of  a  pendulum 
39.1  indies  long  at  the  surface  of  the  moon,  where  the  ac- 
celeration of  gravity  is  only  4.8  ft.  ? 

t  :  f  : :  --  :  -4=    (see  3d  Law  of  Pendulum,  p.  69). 

Vo   vV 


t'  =  2.58  seconds. 

5O.  What   would    be    the  time    of    vibration  for   the 
same  pendulum  at  the  surface  of  the  sun,  where  the  accel- 

*  The  radius,   or  semi-diameter  of  the   earth,  is  given  by  French  as- 
tronomers at  6,366  km. 


22  ANSWERS    TO    PRACTICAL     QUESTIONS 

eration  of  gravity  is  27  times  what  it  is  at  the  earth's  sur- 
face ? 


t'  =  .19  + second. 

51.  How  many  vibrations  per  minute  would  be  made 
at  the  surface  of  the  moon  by  a  pendulum  4O  ft.  long  ? 

First  find  the  time  of  a  single  vibration. 


x  1  2 
.  /  .  .  A/  ""'^  .  A  /  •"  ' 

mt  • '  V  ~W '  V  ~T8~~ 

t  =  9  +  seconds. 

Hence,  in  a  minute,  the  number  of  vibrations  will  be   not 
quite  7. 

52.  A  pendulum  vibrates    2OO  times  in  15  minutes. 
irJiat  is  its  length? 

15x60 

=  4£  seconds,  the  time  of  a  single  vibration. 


x  —  791.8  inches,  or  66  feet  nearly. 

53.  For  a  certain  clock  in  New  York  the  pendulum  was 
made  5OO  Ibs.  in  weight.     JFJiat  was  the  object  in  making 
it  so  heavy  ? 

To  secure  regularity  of  motion  by  means  of  the  large  mass, 
so  that  variations  in  resistance  may  be  avoided  as  nearly  as 
possible. 

54.  Pendulums  are  often  supported  by  knife-edges  of 
steel  resting  on  plates  of  agate.     Why  ? 

Because  the  friction  between  steel  and  agate  is  less  than  if 
any  other  substances  are  used.  It  is  desirable  to  avoid  friction 
as  completely  as  possible. 

55.  The  acceleration  of  gravity  at  the  equator  is  32.O88 
ft. ;  at  the  pole,  32.253ft.    If  a  pendulum  vibrates  3, GOO 
times  an  hour  at  the  equator,  how  many  times  an  hour 
will  it  vibrate  at  the  pole  ? 


IN    POPULAR    PHYSICS.  23 

The  number  of  vibrations  per  hour  varies  inversely  as  the 
time  of  vibration  of  the  pendulum.  For  t  in  the  formula, 
therefore,  we  may  substitute  the  reciprocal  of  the  number  of 
vibrations  per  hour. 

1     .  JL  . .  1_  . 1_ 

3600  '  x"  ^3^088 '  V32T253 
x  =  3,609.36  times. 


THE    MECHANICAL    POWERS. 

94 — 1.  Describe  the  rudder  of  a  boat  as  a  lever. 

The  water  is  the  F,  the  boat  the  "W,  and  the  hand  the  P. 
As  the  W  is  between  the  F  and  the  P,  it  is  a  lever  of  the 
second  class.  By  similar  reasoning  it  is  easy  to  analyze  the 
remaining  cases,  a  door,  a  door-latch,  etc. 

95—2.  Show  the  change  that  occurs  from  the  second  to 
the  third  class  of  levers,  when  you  take  hold  of  a  ladder  at 
one  end  and  raise  it  against  a  building. 

At  first  the  ground  is  the  F  at  one  end,  the  hand  the  P 
at  the  other,  and  the  ladder  the  W  hanging  between ;  hence  this 
is  a  lever  of  the  second  class.  After  a  little,  the  F  remaining 
the  same,  the  P  is  applied  at  one  end,  near  the  F,  and  the 
ladder  is  the  W  hanging  at  the  other  ;  hence  this  is  now  a 
lever  of  the  third  class. 

3.  IVJiy  is  a  pinch  from  the  tongs  near  the  hinge  more 
severe  than  one  near  the  end  ? 

Because  in  the  former  case  the  tongs  are  a  lever  of  the 
first  class— in  the  latter,  of  the  third.  In  the  first  class  there 
is  a  gain  of  power,  in  the  third  a  loss. 

4.  Two  persons    are   carrying  a    weight  of  25 O  lbs.9 
hanging  between  them   from    a  pole  1O    feet  in  length* 
Wliere  should  it  be  suspended  so  that  one  ivill  lift  only  5O 
Ibs.  ? 

One  lifts  50  Ibs.  ;  the  other  200  Ibs.  The  proportionate 
length  of  the  arms  of  the  lever  should  be  the  same  as  the 
proportionate  weights  —  i.e.,  1  to  4.  10-5-5  =  2,  the  unit  of 


24  AXSWEJRS    TO    PRACTICAL     QUESTIONS 

measure.  Hence  one  arm  is  2  feet  long  and  the  other  8  feet 
long.  PROOF.— 50  x  8  =  200  x  2.  This  is  the  substance  also  of 
the  equation  P  x  Pd  =  W  x  Wd. 

5.  In  a  lever  of  the  first  class,  6  feet  long,  where  should 
the  F  be  placed  so  that  a  P  of  1  Ib.  will  balance  a  W  of  23 
Ibs.? 

6  feet  =  72  inches.  72  •*-  24  =  3,  the  unit  of  distance.  The 
W  must  be  placed  3  in.  and  the  P  69  in.  from  the  F.  PROOF. — 
23  x  3  =  1  x  69  (Prob.  4). 

6.  What  P  would  be  required  to  lift  a  barrel  of  pork 
with  a  windlass  whose  ajcle  is  one  foot  in  diameter  and 
handles  ft.  long? 

P  :  W  :  rad.  of  axle  : :  rad.  of  wheel. 

a: :  200  Ibs.  : :  J  ft.  :  3  ft. 

x  =  33£  Ibs. 

7.  What  sized  axle,  with  a  wheel  6  feet  in  diameter, 
would  be  required  to  balance  a  W  of  1  ton  by  a  P  of  JLOO 
Ibs.? 

P  :  W  : :  diameter  of  axle  :  diameter  of  wheel. 

100  Ibs.  :  2,000  Ibs.  :  :  x  :  6  ft. 

x  =  T%  ft.  =  the  diameter. 

8.  What  number  of  movable  pulleys  would  be  required 
to  lift  a  W  of  200  Ibs.  with  a  P  of  25  Ibs.  ? 

W  =  P  x  twice  the  number  of  movable  pulleys  ; 

W 
hence  -p-  =  twice  the  number  of  movable  pulleys. 

200  -4-25  =  8.     8  -*-  2  =  4  =  the  number  required. 

9.  How  many  Ibs.  could  be  lifted  with  a  system  of  4 
movable  pulleys,  and  one  fixed  pulley  to  change  the  direc- 
tion of  the  force,  by  a  P  of  1OO  Ibs.  ? 

W  =  P  x  twice  the  number  of  movable  pulleys. 
100  Ibs.  x  (4  x  2)  =  800  Ibs.  =  the  W. 


IN    POPULAR    PHYSICS.  25 

10.  What  weight  could  be  lifted  with  a  single  horse 
power  (3 3 ,OOO  Ibs.  one  foot  high  per  minute)  acting  on  a 
system  of  pulleys  shown  in  Fig.  62  ? 

"W  =  33,000 x2x2x2x2=  528,000  Ibs. 

11.  What  distance  should  there  be  between  the  threads 
of  a  screiv,  that  a  P  of  25  lbs.9  acting  on  a  handle  3  ft. 
long,  may  lift  1  ton  weight? 

P  :  W  : :  Interval :  Circumference. 

25  Ibs.  :  2,000  Ibs.  : :  x  :  72  in.  x  3.1416. 

x  =  2.83  -in. 

12.  How  high  could  a  P  of  12  Ibs.,  moving  16  ft.  along 
an  inclined  plane,  lift  a  W  of  96  Ibs.  ? 

P  :  W  : :  height :  length. 

12  Ibs.  :  96  Ibs.  : :  x  :  16  ft. 

X  =  2  ft. 

13.  I  wish  to  roll  a  barrel  of  flour  into  a  wagon,  the 
booc  of  which  is  4  ft.  from  the  ground.    I  can  lift  but  24= 
Ibs.    How  long  a  plank  should  I  get  ? 

P  :  W  : :  height :  length. 
24  Ibs.  :  196  Ibs.  : :  4  ft.  :  x  =  32f  ft. 

14.  What  Wean  be  lifted  with  a  P  of  1OO  Ibs.  acting 
on  a  screw  having  threads  1  in.  apartt  and  a  handle  4  ft. 

long? 

P  :  "W  : :  Interval :  Circumference. 

100:  x::  1  :  4x12x3.1416 
x  =  15,079.68. 

15.  What  is  the  object  of  the  balls  often  cast  on  the  ends 
of  the  handle  of  the  screw  used  in  presses  for  copying  let" 
ters  ? 

By  their  momentum  they  make  the  motion  more  uniform 
and  continuous. 

16.  In  a  steelyard  2  ft.  long,  the  distance  from  the 
weight-hook  to  the  fulcrum-hook  is  2  in.     How  heavy  a 
body  can  be  weighed  with  a  1  Ib.  weight  ? 

24  in.-  2  in.  =  22  in.     1  Ib.  x  22  =  22  Ibs.  =  P. 
22  Ibs.  -*-2=  11  Ibs.  =W. 


26  ANSWERS    TO    PRACTICAL     QUESTIONS 

17.  Describe  the  change  from  the  1st  to  the  3d  class  of 
levers,  in  the  different  ivays  of  using  a  spade. 

When  digging,  the  ground  at  the  back  of  the  spade  is  the 
F  ;  the  ground  lifted  is  the  W  ;  and  the  hand  at  the  other  end 
is  the  P.  As  the  "W"  is  at  one  end,  P  at  the  other,  and  the  P 
between,  this  is  a  lever  of  the  1st  class.  When  throwing  dirt, 
the  left  hand  at  one  end  of  the  spade  is  the  P  ;  the  dirt  at  the 
other  end  is  the  W,  and  the  right  hand  between  the  two  is  the 
P.  As  the  P  is  between  the  P  and  the  W,  this  is  a  lever  of 
the  3d  class. 

18.  Wliy  are  not  blacksmiths'  tongs  and  fire  tongs  con- 
structed on  the  same  principle  ? 

The  former  are  of  the  1st  class,  as  power  is  required  :  the 
latter  of  the  3d  class,  as  rapidity  only  is  necessary. 

19.  In  a  lever  of  the  3d  class,  what  W  will  a  P  of  5O 
Ibs.  balance,  if  one  arm  is  12ft.  and  the  other  3  ft.  long? 


50  Ibs.  :  x  :  :  12  ft.  :  3  ft. 
x  =  12|-  Ibs. 

96—  2O.  In  a  lever  of  the  2d  class,  ivhat  W  will  a  P  of 
50  Ibs.  balance,  with  a  lever  12  feet  long  and  W  3  feet 
from  the  F? 

50  Ibs.  :  x::  3ft.  :  12ft. 
x  =  200  Ibs. 

21.  In  a  lever  of  the  1st  class,  what  W  will  a  F  of  5O 
Ibs.  balance,  with  a  lever  12  ft.  long  and  the  F  3  ft.  from 
the  W? 

50  Ibs.  :  x  :  :  3  ft.  :  9  ft. 
x  =  150  Ibs. 

22.  In  a  wheel  and  axle,  the  F  =  4O  Ibs.,  W  =  36O  Ibs., 
diameter  of  aocle  =  #  in.    Required  the  circumference  of 
the  wheel. 

P  :  W  :  :  diameter  of  axle  :  diam.  of  wheel. 

40  Ibs.  :  360  Ibs.  :  :  8  in.  :  x  =  72  in.  =  6  ft.,  the  diameter  of  wheel. 
6  ft.  x  3.1416  =  18.85  ft.,  the  circumference  of  the  wheel. 


7JV   POPULAR    PHYSICS.  27 

23.  Suppose  in  a  wheel  and  axle  the  P  —  2O  Ibs.,  the  W— 
24O  Ibs.,  and  the  diameter  of  wheel  =  4  ft.    Required  the 
circumference  of  the  axle. 

20  Ibs.  :  240  Ibs.  : :  x  :  48  in. 
x  =  4  in.  (diameter  of  axle). 
4  in.  x  3.1416  =  12.56  in.  (circumference). 

24.  Hequired ,  in  a  tvheel  and  axle,  the  diameter  of  the 
wheel,  the  diameter  of  the  axle  being  1O  inches,  P  —  1OO 
Ibs.  and  W  =  1  ton. 

100  Ibs.  :  2,000  Ibs.  : :  10  in.  :  x  =  200  in.  =  16f  ft. 

25.  Why  is  the  rim  of  a  fly -wheel  made  so  Jieavy  ? 

The  largest  momentum  possible  is  desired.  The  velocity  of 
a  particle  is  proportional  to  its  radius  in  rotation.  Hence  the 
largest  part  of  the  mass  of  the  wheel  is  fixed  at  the  rim. 

26.  Describe   the  hammer,  when  used  in  drawing  a 
nail,  as  a  bent  lever,   i.e.,  one  in  which  the  bar  is  not 
straight. 

If  a  lever  is  bent,  or  if,  when  it  is  straight,  the  bar  is  not 
at  right  angles  to  the  lines  of  action  of  the  P  and  the  W,  it  is 
necessary  to  distinguish  between  the  arms  of  a  lever  and  the 
arms  of  the  P  and  the  "W,  regarded  as  forces  which  have  mo- 
ments around  the  F.  In  the  latter  sense,  the  arms  are  the  per- 
pendiculars, dropped  from  the  F  to  the  lines  of  action  of  the 
P  and  the  W. 

27 •  Describe  the  four  levers  shown  in  Fig.  46,  when 
both  the  load  of  hay  and  the  weight  are  considered,  re- 
spectively, as  the  W  and  the  P. 

This  is  so  fully  answered  in  the  text  that  no  further  expla- 
nation seems  necessary.  The  pupil  should  be  required  to  as- 
sume values  for  the  W  and  for  each  of  the  lever  arms,  and 
compute  the  weight  of  the  wagon  and  hay  together.  Call  his 
attention  to  the  fact  that  half  the  weight  of  the  wagon  and 
hay  is  transmitted  at  the  point  P,  and  the  other  half  at  P' ; 
also  that  the  vertical  rod  at  the  lift  serves  only  as  a  connector, 
and  not  as  a  lever. 


28  AXSWJEKS    TO    PRACTICAL 


HYDROSTATICS. 

I  1 9 — !•  Why  can  housekeepers  test  the  strength  of  lye, 
by  trying  ivhether  or  not  an  egg  ivill  float  on  it  ? 

The  potash  dissolved  in  the  water  to  form  lye  increases  the 
density  of  the  liquid.  When  enough  has  been  dissolved  to  make 
its  specific  gravity  greater  than  that  of  the  egg,  the  egg  will 
float.  This  becomes,  therefore,  a  simple  but  rough  means  of 
testing  the  amount  of  potash  contained  in  the  lye. 

2.  Hoiv  much  water  will  it  take  to  make  a  gallon  of 
strong  brine  ? 

A  gallon.  The  salt  does  not  increase  the  volume  of  the 
liquid. 

3.  Why  ought  a  fat  man  to  swim  more  easily  than  a 
lean  one  ? 

Because  muscles  and  bones  are  heavier  than  fat.  The  spe- 
cific gravity  of  a  fat  man  is,  therefore,  less  than  that  of  a  lean 
one. 

0.  If  ^ve  let  bubbles  of  air  pass  up  through  a  jar  of 
water9  why  will  they  become  larger  as  they  ascend  ? 

The  pressure  of  the  water  is  less  as  they  near  the  top,  and 
so  they  expand. 

7.  IFJiat  is  the  pressure  on  a  canal  lock-gate  14  feet 
high  and  lOfeet  wide,  ^vhen  the  lock  is  full  of  water  ? 

14  x  10  x  7  x  1,000  oz.  =  980,000  oz.  =  61,250  Ibs. 

8.  Will  a  pail  of  ivater  'weigh  any  more  with  a  live  fish 
in  it  than  without  ? 

If  the  pail  were  full  before  the  fish  was  put  in,  then  it  will 
make  no  difference,  since  the  fish  will  displace  its  own  weight 
of  water,  which  will  run  over.  If  the  pail  is  only  partially 
filled,  then,  though  the  fish  is  upheld  by  the  buoyancy  of  the 
water,  since  action  is  equal  to  reaction,  it  adds  its  own  weight 
to  that  of  the  water. 


IN   POPULAR    PHYSICS.  29 

9.  If  the  ivater  filtering  down  through  a  rock  should 
colled  in  a  crevice  an  inch  square  and  25O  feet  high,  open- 
ing at  the  bottom  into  a  closed  fissure  having  2 O  square 
feet  of  surface,  what  would  be  the  total  pressure  tending  to 
burst  the  rock? 

Neglecting  the  diameter  of  the  fissure,  the  pressure  is  the 
same  on  every  square  inch  of  the  twenty  square  feet  of  sur- 
face. 

j^  250  x  1,000  oz.x  20x144  =  31 
144  >  1 1^ 

10.  Why  can  stones  in  water  be  moved  so  much  more 
easily  than  on  land? 

Because  the  water  buoys  up  nearly  one  half  of  their 
weight. 

11.  IVliy  is  it  so  difficult  to  wade  in  the  water  where 
there  is  any  current  ? 

Because  we  have  to  move  not  only  the  weight  of  our  own 
bodies,  but  also  the  water.  The  kinetic  energy  of  this  is  pro- 
portional to  the  mass  displaced,  and  to  the  square  of  its  velocity. 

1 2O — 12.  Wliy  is  a  mill-dam  or  a  canal  embankment 
made  small  at  the  top  and  large  at  the  bottom  ? 

Because  the  pressure  of  the  water  increases  with  the  depth. 

13.  In  digging  canals,  ought  the  engineer  to  take  into 
consideration  the  curvature  of  the  earth  ? 

There  is  no  necessity  to  do  so.  A  water  level  is  in  practice 
assumed  to  be  horizontal.  In  geodetic  surveys,  like  that  of  the 
coast  line  of  a  country,  allowance  has  to  be  made  for  the  cur- 
vature of  the  earth.  Station  points  twenty  miles  apart,  or 
more,  are  taken,  between  which  the  earth's  curvature  is  readily 
calculable  and  perceptible. 

14.  Why  does  the  bubble  of  air  in  a  spirit-level  move 
as  the  instrument  is  turned  ? 

Because  the  air  is  lighter  than  the  alcohol,  and  rises  con- 
stantly to  the  highest  point.  For  this  reason,  also,  the  tube  is 
curved  so  as  to  be  convex  at  the  center. 


30  ANSWERS    TO    PRACTICAL     QUESTIONS 

15.  Can  a  swimmer  tread  on  pieces  of  glass  at  the  bot- 
tom of  the  ivater  with  less  danger  than  on  land  ? 

Yes.     But   he  would  still  find  it   unadvi  sable  to  try  the  ex- 
periment. 

16.  Will  a  vessel  displace  more  water  in  a  fresh  river 
than  in  the  ocean  ? 

In  the  fresh   river,  because  the  specific  gravity,  and  hence 
the  buoyancy,  of  fresh  water  is  less. 

17.  Will  iron  sink  in  mercury  ? 

No.     It  will  float,  like  a  cork  on  water. 

18.  The  water  in  the  reservoir  in  Neiv  York  is  about  SO 
feet  above  the  fountain  in  the  City  Hall  Park.     What  is 
the  pressure  on  a  single  inch  of  the  pipe  at  the  latter  point  ? 

(1,000  oz.  x  80)  H-  144  =  34.7  Ibs. 

19.  Why  does  cream  rise  on  milk  ? 

Because  it  is  lighter  than  the  milk. 

20.  Ttiere  is  a  story  told  of  a  Chinese  boy  who  accident- 
ally dropped  Jiis  ball  into  a  deep  hole,  where  he  could  not 
reach  it.    He  filled  the  hole  with  water,  but  the  ball  ivould 
not  quite  float.    He  finally  bethought  himself  of  a  lucky 
expedient,  which  was  successful.    Can  you  guess  it  ? 

He  put  salt  in  the  water. 

21.  Which  has  the  greater  buoyant  force,  oil  or  water  ? 

Water,  because  its  density  is  greater. 

22.  What  is  the  weight  of  4=  cu.  ft.  of  cork  ? 

1,000  oz.  =  the  weight  of  1  cu.  ft.  of  water. 
.240  =  the  spec.  grav.  of  cork. 

240  oz.  =  the  weight  of  1  cu.  ft.  of  cork. 
4 


960  oz.  =  the  weight  of  4  cu.  ft,  of  cork, 
=  60  Ibs. 


IN   POPULAR    PHYSICS.  31 

23.  How  many  oz.  of  iron  will  a  cubic  foot  of  cork  float 
in  water  ? 

1,000  oz.  =  weight  of  a  cubic  foot  of  water. 
.240        =  spec.  grav.  of  cork. 

240        =  weight  of  a  cubic  foot  of  cork. 
1,000  oz.  —  240  oz.  =  760  oz.,  the  buoyant  force  of  a  cubic  foot. 

24.  IVJiat  is  the  specific  gravity  of  a  body  whose  weight 
in  air  is  3O  grs.  and  in  water  2O  grs.  <? 

30  grs.  —  20  grs.  —  10  grs. 

30  grs.  H-  10  grs.  =  3. 
The  body  is  three  times  as  heavy  as  water. 

25.  Which  is  heavier,  a  pail  of  fresh-water  or  one  of 
salt-water  ? 

A  pail  of  salt-water  is  as  much  heavier  than  one  of  fresh- 
water as  the  weight  of  the  salt  added  to  make  the  brine. 

26.  Tlie  weights  of  a  piece  of  syenite-rock  in  air  and  in 
water  were  3941.8  <jrs.  and  26O7.5  grs.     Find  its  spec, 
grav. — Ans.  2.954. 

27 •  A  specimen  of  green  sapphire  from  Slam  weighed 
in  air  21.45  grs.9  and  in  water  16.33  grs.  Required  its 
spec.  grav. — Ans.  4.189. 

28.  A  specimen  of  granite  weighs  in  air  534.8  grs., 
and  in  water  334.6  grs.     Wliat  is  the  spec,  grav.?— Ans. 
2.671. 

29.  What  is  the  volume  of  a  ton  of  iron  ? 

1,000  oz.  =  weight  of  1  cu.  ft.  of  water 
7.8         —  spec.  grav.  of  iron. 

7,800  oz.  =  weight  of  a  cu.  ft.  of  iron. 
32,000  oz.  (a  ton  of  iron)  -*-  7,800  (weight  of  a  cu.  ft.)  =  4/g-  cu.  ft. 


32  ANSWERS    TO    PRACTICAL     QUESTIONS 

A  ton  of  gold  ? 

1,000  oz.  =  weight  of  a  cu.  ft.  of  water. 

19.34  =  spec.  grav.  of  gold. 
19,340  oz.  *  —  weight  of  a  cu.  ft.  of  gold. 
32,000  oz.*  -4-  19,340  oz.  =  1.6,  the  no.  of  cu.  ft. 

A  ton  of  copper  ? 

1,000  oz.  x  8.9  =  8,900  oz. 
32,000  oz.  -f-  8,9QO  oz.  =  3.6  (nearly)  the  no.  of  cu.  ft. 

30.  WJiat  is  the  weight  of  a  cube  of  gold  4  feet  on  each 
side? 

43  =  64,  the  no.  of  cu.  ft. 

19,340  oz.*  (no  of  oz.  in  1  cu.  ft.)  x  64  =  77,360  Ibs. 

31.  A  cistern  is  12  ft.  Iong9  G  ft.  wide,  and  1O  ft.  deep. 
When  full  of  water,  what  is  the  pressure,  on  each  side? 

On  one  side,  12  x  10  x  5  x  1,000  oz.  =  600,000  oz.  =  37,500  Ibs. 
On  one  end,  6  x  10  x  5  x  1,000  oz.  =  300,000  oz.  =  18,750  Ibs. 

32.  Why  does  a  dead  fish  always  float  on  its  back  ? 

It  has  its  swimming-bladder  located  just  under  the  spine  ; 
and  this  is  the  lightest  part  of  its  body,  and,  of  course,  comes 
to  the  top  as  soon  as  the  fish  dies. 

34.  A  vessel  holds  1O  Ibs.  of  'water  ;   how  much  mer- 
cury would  it  contain  ? 

Mercury  is  13.5  times  heavier  than  water.  Hence  the  vessel 
would  contain  10  Ibs.  x  13.5  =  135  Ibs.  of  mercury. 

35.  A  stone  weighs  70  Ibs.  in  air  and  5O  in  water. 
What  is  its  bulk  ? 

70  —  50  =  20.     20  x  16  oz.  =  320  oz.,  the  weight  of  water  displaced. 
320  oz.  is  ^  of  a  cu.  ft. 


*  In  these  solutions  the  student  should  notice  that  avoirdupois 
is  used  in  weighing  the  gold.  To  be  exact,  1,000  oz.,  the  weight  of  a  cu. 
ft.  of  water,  should  be  reduced  to  Troy  weight,  and  the  Ib.  gold  taken  «* 
12  oz.  Troy,  when  the  answer  would  be  about  1.36  cu.  ft. 


IN   POPULAR    PHYSICS.  33 

56*.  A  hollow  ball  of  iron  weighs  1O  Ibs. :  what  must  be 
its  volume  to  float  in  water  ? 

10  Ibs.  =  160  oz.  As  a  cubic  ft.  of  water  weighs  1,000  oz., 
the  ball  must  displace  such  a  part  of  a  cu.  ft.  of  water  as  160 
oz.  is  of  1,000  oz.,  or  .16  cu.  ft. 

37.  Suppose  that  Hiero's  crown  was  an  alloy  of  silver 
and  gold,  and  weighed  22  oz.  in  air  and  2O%  oz.  in  water. 
What  was  the  proportion  of  each  metal  ? 

"Multiply  the  specific  gravity  of  each  ingredient  by  the 
difference  between  it  and  the  specific  gravity  of  the  compound. 
As  the  sum  of  the  products  is  to  the  respective  products,  so  is 
the  specific  gravity  of  the  body  to  the  proportions  of  the  in- 
gredients. Then,  as  the  specific  gravity  of  the  compound  is  to 
the  weight  of  the  compound,  so  is  each  of  the  proportions  to 
the  weight  of  its  material." — American  Cyclopedia. 

Second  method : 

Let  A  =  mass  of  crown  =  22 

"  B  =  sp.  gr.        "        =  14.66 

"  x  =  mass  of  gold 

"  x'  =  sp.  gr.    "  =  19.26 

"  y  =  mass  of  silver 

"  y1  =  sp.  gr.     "  —  10.5 

then 

and  since 

mass 
volume  =  — 


specific  gravity' 
we  have 

A  _x     y  f 

B"-tfV 

whence  we  find  (approximately), 

Gold    =  13.95 
Silver  =    8.05 

1 2 1  —  38.  Wliy  ^vill  oilf  which  floats  on  water,  sink  in 
alcohol  ? 

The  specific  gravity  of  absolute  alcohol  is  only  .79  ;  hence 
even  the  dilute  alcohol  of  commerce  is  lighter  than  most  speci- 
mens of  oil. 


34  ANSWERS    TO    PRACTICAL     QUESTIONS 

39.  A  specific-gravity  bottle  holds  1OO  gms.  of  ^vater 
and  ISO  gms.  of  sulphuric  acid.    Required  the  density  of 
the  acid.  —  Ans.  1.8. 

40.  Wliat  is  the  density  of  a  body  which  weighs  58  gins. 
in  air  and  46  gms.  in  water  ?  —  Ans.  4f  . 

41.  What  is  the  density  of  a  body  which  iveighs  63 
guns,  in  air  and  35  gms.  in  a  liquid  of  a  density  of  .85  ?  — 
Ans.  1.9125. 

HYDRODYNAMICS. 

129—  1.  Two  faucets,  one  8  feet  and  the  other  4  feet  be- 
low the  surface  of  the  water  in  a  cistern,  are  kept  open  for 
a  minute.  How  many  times  as  much  water  can  be  drawn 
from  the  first  as  the  second  ? 


Hence  the  first  delivers  rather  more  than  41$  more  than 
the  second. 

2.  How  much  water  will  be  discharged  per  second  from 
a  short  pipe  having  a  diameter  of  4  inches  and  a  depth 
of  48  feet  below  the  surface  of  the  ^vater? 

The  cross  section  of  the  pipe  is  16  x  .7854  =  12.57  sq.  inches, 
=  .087  sq.  feet.  _ 

v  =  ^/'2gh  =  -v/64  x  48  =  55.4 
55.  4  x.  087  =  4.8  cu  ft. 

3.  When  we  pour  molasses  from  a  jug,  why  is  the 
stream  so  much  larger  near  the  nozzle  than  at  some  dis- 
tance from  it  ? 

Because,  according  to  the  law  of  falling  bodies,  the  farther 
the  molasses  fajls  the  faster  it  falls.  The  stream,  therefore, 
becomes  smaller  as  it  moves  more  swiftly,  until,  at  last,  it 
breaks  up  into  drops. 

4.  Ought  a  faucet  to  extend  into  a  barrel  beyond  the 
staves  ? 


IN    POPULAR    PHYSICS.  35 

No  ;  this  would  cause  more  friction,  and  increase  the  resist- 
ance to  outflow  produced  by  cross  currents. 

5.  What  ivould  be  the  effect  if  both  openings  in  one  of 
the  arms  of  Barker's  Mill  were  on  the  same  side  ? 

It  would  cease  revolving.  The  pressure  in  each  direction 
would  then  be  equal,  and  the  arms  would  balance. 

PNEUMATICS. 

1 45 — 1.  Why  must  we  make  tivo  openings  in  a  barrel 
of  cider  when  we  tap  it  ? 

One  to  let  out  the  cider,  and  one  to  admit  the  air. 

2.  What  is  the  weight  of  1O  cubic  feet  of  air  ? 

100  cu.  in.  weigh  31  grs.  ;  hence  10  cu.  ft.  will  weigh  31  grs. 
x  172.8  =  .7652  Ibs.  avoirdupois. 

3.  What  is  the  pressure  of  the  air  on  one  square  rod  of 
land  ? 

2721  x  144  x  15  Ibs.  =  588,060  Ibs. 

4.  What  is  the  pressure  on  a  pair  of  Magdeburg  hemi- 
spheres 4  in.  in  diameter,  when  the  air  is  entirely  ex- 
hausted ? 

On  each  hemisphere  the  pressure  is  equal  to  the  area  of  a 
great  circle,  multiplied  by  the  pressure  on  each  unit  of  area. 
Hence  on  each  hemisphere  the  pressure  is 

.7854  x  42  x  15  Ibs.  =  188.5  Ibs.  nearly. 
The  sum  of  the  two  opposite  pressures  is  thus  not  quite  277  Ibs. 

5.  Hoiv  high  a  column  of  water  can  the  air  sustain 
when  the  barometric  column  stands  at  28  in.  ? 

28  in.  x  13^  =  31£  feet. 

6.  Tf  we  should  add  a  pressure   of  two  atmospheres, 
what  ivould  be  the  volume  of  1OO  cu.  in.  of  common  air  ? 

The  pressure  is  trebled,  and,  according  to  Mariotte's  law,  the 
volume  will  be  reduced  in  the  same  proportion ;  hence  it  will 
be  100  cu.  in.  H-  3  =  33*-  cu.  in. 


36  ANSWERS    TO    PRACTICAL     QUESTIONS 

146—7.  If 9  while  the  water  is  running  through  the 
siphon,  we  quickly  lift  the  long  arm,  what  will  be  the  effect 
on  the  water  in  the  siphon  ?  If  we  lift  the  entire  siphon  ? 

The  question  assumes  the  siphon  to  be  flexible.  If  the  bot- 
tom of  the  long  arm  be  below  that  of  the  short  arm,  the  water 
flows  through  it  toward  the  lower  level.  By  lifting  it  the  rate 
of  flow  diminishes  until  its  level  is  the  same  as  that  of  tho 
short  arm.  On  lifting  it  still  higher,  the  water  contained  in  the 
siphon  flows  back  through  the  short  arm,  and  the  siphon  is 
thus  emptied.  If,  however,  the  whole  siphon  is  lifted,  it  is 
emptied  through  the  long  arm. 

8.  WJien  the  mercury  stands  at  29\  in.  in  the  barome- 
ter, how  high  above  the  surface  of  the  ivater  can  ive  place 
the  lower  pump-valve  ? 

In  theory,  29^  in.  x  13£  =  398}  in.;  in  practice,  the  distance 
is  much  less  than  this. 

9.  Can  we  raise  water  to  a  higher  level  by  means  of  a 
siphon  ? 

There  is  no  power  in  a  siphon  ;  it  is  only  a  way  of  guiding 
the  flow  of  water  to  a  lower  level. 

10.  If  the  air  in  the  chamber  of  a  fire-engine  be  con- 
densed to  TV  its  former  bulk,  what  will  be  the  pressure  due 
to  the  expansive  force  of  the  air  on  every  square  inch  of 
the  air-chamber  ? — Ans.  24O  Ibs. 

11.  IVtiat  causes  the  bubbles  to  rise  to  the  surface  when 
we  put  a  lump  of  loaf-sugar  in  hot  tea  ? 

The  bubbles  of  air  contained  in  the  pores  of  the  sugar  rise 
because  they  are  lighter  than  the  water. 

12.  When  will  a  balloon  stop  rising  ?    IVJiat  weight  can 
it  lift  ? 

It  will  stop  rising  when  the  weight  of  the  balloon  and  its 
contents  is  just  equal  to  that  of  the  same  volume  of  rarefied 
air  which  it  displaces.  It  can  lift  a  weight  equal  to  the  dif- 
ference between  the  weight  of  the  hydrogen  or  coal  gas  with 
which  it  is  filled  and  that  of  the  air  in  which  it  is  immersed, 
minus  the  weight  of  the  balloon  itself. 


IN    POPULAR    PHYSICS.  37 

14.  When  smoke  ascends  in  a  straight  line,  is  it  a  proof 
of  the  rarity  or  density  of  the  air  ? 

Of  its  density,  because  it  shows  that  the  smoke  is  much 
lighter  than  the  air,  and  so  rises  immediately. 

15.  Explain  the  action  of  the  common  leather-sucker. 

There  is  nearly  a  vacuum  between  the  sucker  and  the  slab, 
which  is  buoyed  up  by  the  pressure  of  the  air  beneath. 

16.  Did  you  ever  see  a  bottle  really  empty  ? 

No.    No  absolute  vacuum  has  ever  been  produced  in  a  bottle 
or  any  other  vessel  by  human  agency,  so  far  as  is  known. 

18.  How  does  the  variation  in  the  pressure  of  the  air 
affect  those  ^vho  ascend  lofty  mountains  ?     Who  descend  in 
diving  bells? 

The  outward  pressure  at  a  great, elevation  is  partly  removed, 
and  the  inner  pressure  remaining  the  same,  the  blood  is  often 
forced  through  the  ears,  nostrils,  etc.  When  one  descends  into 
a  deep  mine  the  conditions  are  reversed  :  the  outer  pressure  be- 
comes in  excess  of  the  inner  ;  severe  pain  is  felt  in  the  ear-drum, 
and  ringing  noises  in  the  head  become  almost  intolerable.  These, 
however,  disappear  after  a  time,  when  the  equilibrium  between 
the  internal  and  external  pressure  is  restored.  It  is  said  that 
Humboldt  ascended  where  the  mercurial  column  fell  to  14  inches, 
and  descended  in  a  diving-bell  where  it  rose  to  45  inches — thus 
making  a  variation  of  31  inches,  or  a  difference  of  31,000  Ibs. 
pressure  on  the  body. 

19.  Explain  the  theory  of  t(  sucking  cider  "  through  a 
straw. 

By  the  action  of  the  muscles  of  the  chest  the  lungs  are 
made  to  expand.  A  partial  vacuum  in  them  is  thus  produced, 
and  the  pressure  of  the  air  hence  forces  liquid  through  the 
straw  up  into  the  mouth.  By  closing  the  glottis  at  the  right 
moment  this  is  prevented  from  going  through  the  windpipe, 
and  it  is  at  once  swallowed. 

20.  Would  it  make  any  difference  in  the  action  of  the 
siphon  if  the  limbs  were  of  unequal  diameter  ? 


38  AXSWEKS    TO    PRACTICAL     QUESTIONS 

The  flow  of  water  through  the  narrower  part  of  the  siphon 
would  be  faster  than  through  the  wider  part. 

21.  What  would  be  the  effect  of  malting  a  small  hole  in 
the  top  of  a  diving-bell  while  in  use  ? 

It  would  allow  the  compressed  air  to  be  pushed  out  by  the 
pressure  of  the  water  below. 

22.  The  pressure  of  the  atmosphere  being  1.O3  kg.  per 
sq.  cm.9  what  is  the  amount  on  1O  sq.  meters  ? 

103,000  kg. 

ACOUSTICS. 

184 — 1.  Why  can  not  the  rear  of  a  long  column  of 
soldiers  keep  time  to  the  music  ? 

Because  it  takes  time  for  the  sound-wave  to  pass  down  the 
column,  and  hence  those  in  the  rear  do  not  hear  the  music  as 
soon  as  those  in  front. 

2.  Three  minutes  elapse  between  the  flash  and  the  re- 
port of  a  thunderbolt :  hoiv  far  distant  is  it  ? 

If  the  air  is  at  the  freezing  point,  the  distance  is 
1,090  ft,  x  60  x  3  =  196,200  ft. 

5.  Five  seconds  expire  between  the  flash  and  report  of 
a  gun:  what  is  the  distance? 

1,090  ft.  x  5  =  5,450  ft. 

4.  Suppose  a  speaking-tube  should  connect  tivo  villages 
1O  miles  apart.  How  long  would  it  take  a  sound  to  pass 
that  distance  ? 

52,800  ft  +-  1,090  ft.  =  48.4  (sec.) 

This  is  of  course  a  theoretical  case.  The  initial  energy 
manifested  as  sound  would  be  transformed  into  other  modes  of 
energy,  such  as  heat,  before  complete  transmission  through  so 
great  a  distance  in  a  speaking-tube,  unless  the  sound  be  more 
intense  than  that  of  the  human  voice  usually  is. 


IN   POPULAR    PHYSICS.  39 

5.  The  report  of  a  pistol-shot  was  returned  to  the  ear 
from  the  face  of  a  cliff  in  4:  seconds.  Hoiv  far  was  it  ? 

.1,090ft.  x2  =  2, 180  ft. 

6*.  What  is  the  cause  of  the  difference  in  the  voice  of 
man  and  wom,an  ? 

Probably  the  difference  depends  largely  on  the  thickness 
and  length  of  the  vocal  chords.  The  difference  between  a  bass 
and  a  tenor,  a  contralto  and  a  soprano,  depends  largely  also  on 
quality,  just  as  the  sound  of  the  flute  and  violin  on  the  same 
note  is  recognizably  different. 

7.  What  is  the  number  of  vibrations  per  second  neces- 
sary to  produce  the  fifth  tone  of  the  scale  of  Cs  ? 

C3  =  256  vibrations. 
256  x  f  =  384. 

8.  Wliat  is  the  length  of  each  sound-wave  in  that  tone 
ivhen  the  temperature  is  zero  F.  ? 

1,090  ft. -32  ft.  =  1,058  ft.  1,058  -f-  384  =  2  ft.  9  in.  (the  length 
of  each  wave). 

9.  What  is  the  number  of  vibrations  in  the  fourth  tone 
above  C3  ? 

C2  =  128  vibrations. 
128  xf  =192. 

lO.Ifa  meteor  were  to  explode  at  a  height  of  60  miles, 
ivould  it  be  possible  for  its  sound  to  be  heard  at  sea-level  ? 

No.  At  such  a  height  the  atmosphere  would  be  more  rare 
than  in  the  best  vacuum  over  produced  by  human  means.  The 
explosion  would  produce  a  sound  far  too  faint  to  be  audible. 

11.  A  stone  is  let  fall  into  a  well,  and  in  four  seconds  is 
heard  to  strike  the  bottom  ;  hoiv  deep  is  the  ^vell  ? 

Disregarding  the  minute  interval  required  for  the  transmis- 
sion of  the  sound, 

S  =     P  =  16  x  42  =  256  feet. 


40  ANSWERS    TO    PRACTICAL     QUESTIONS 

12.  What  time  would  be  required  for  a  sound  to  travel 
five  miles  in  the  still  water  of  a  lake  ? 

s       5x5,280 
*  =      =  -=  5-6  seconds. 


13.  Does  sound  travel  faster  at  the  foot  or  at  the  top  of 
a  mountain? 

The  density  and  elasticity  of  the  air  vary  in  the  same  pro- 
portion ;  hence  if  the  temperature  were  the  same  on  top  of  a 
mountain  that  it  is  at  the  foot,  the  velocity  of  sound  would  be 
the  same,  but  as  it  is  always  colder,  the  velocity  is  less. 

14.  IVJiy  is  an  echo  weaker  than  the  original  sound  ? 

Because  the  intensity  of  the  sound-wave  is  weakened  at  each 
reflection.  In  addition  to  this,  the  sound  which  is  perceived  as 
an  echo  has  traveled  over  a  much  greater  distance  than  that 
which  comes  directly  from  the  sonorous  body. 

15.  IVlvy  is  it  so  fatiguing  to  talk  through  a  speaking  - 
trumpet  ? 

Because  it  is  unusual,  and  unusual  effort  is  necessary  to  se- 
cure adaptation  to  unusual  conditions. 

16.  WJiy  will  the  report  of  a  cannon  fired  in  a  valley  be 
heard  on  the  top  of  a  neighboring  mountain  better  than 
one  fired  on  the  top  of  a  mountain  will  be  heard  in  the 
valley  ? 

A  sound  always  has  the  intensity  given  it  by  the  density  of 
the  atmosphere  where  it  originated,  and  not  of  that  where  it  is 

heard. 

(See  Tyndall's  Lectures  on  Sound,  p.  40.) 

17.  Why   do   our  footsteps  in  unfurnished  dwellings 
sound  so  startlingly  distinct  ? 

'  In  furnished  rooms,  the  chairs,  carpets,  pictures,  etc.,  break 
up  the  echoes.  Then,  also,  our  footsteps  are  louder  on  an  un- 
carpeted  floor. 

18.  Why  do  the  echoes  of  an  empty  church  disappear 
when  the  audience  assemble  ? 


IN    POPULAR    PHYSICS.  41 

The  audience  break  up  the  echoes  which  interfere  with  the 
original  sound.  Wires  strung  across  a  lofty  room  often  serve 
the  same  purpose  to  a  slight  extent. 

19.    What   is   the  object  of  the  sounding -board  of  a 


By  its  vibrations   and  those  of  the  body  of  air  which  it  in- 
closes, it  re-enforces  the  sound  of  the  wires. 

20.  During  some  experiments,  Tyndall  found  that  a 
certain  sound  would  pass  through  twelve  folds  of  a  dry 
silk  handkerchief,  but  ivould  be  stopped  by  a  single  fold  of 
a  wet  one.    Explain. 

(See  TyndalTs  Lectures  on  Light,  p.  325,  for  a  series  of  experiments  show- 
ing the  action  of  moisture  on  the  propagation  of  sound-waves.) 

21.  What  is  the  cause  of  the  musical  murmur  often 
heard  near  telegraph  lines? 

It  is  produced  by  the  vibration   of  the  wires.     These    are 
thrown  into  motion  by  the  wind  and  other  causes. 

22.  Why  will  a  variation  in  the  quantity  of  ^vater  in 
a  goblet,  when  caused  to  sound,  make  a  difference  in  the 
tone  ? 

It  changes  the  area  of  the  vibrating  portion  of  the  glass. 

23.  At  what  rate  (in  meters)  will  sound  move  through 
air  at  sea-level,  the  temperature  being  2O°  C.  ? 

Sound  moves  at  the  rate  of  1,090  feet  at  0°  C.    The  differ- 
ence is  nearly  2  feet  for  each  degree  C. 

1,090  feet +  40  feet  =1,130  feet. 


OPTICS. 

235 — 1.  Why  is  a  secondary  bow  fainter  than  the  pri- 
mary ? 

The  primary  is  produced  by  one  reflection  and  two  refrac- 
tions ;  the  secondary,  by  two  reflections  and  two  refractions. 
The  additional  reflection  weakens  the  ray 


42  ANSWERS    TO    PRACTICAL     QUESTIONS 

Wliy  are  the  colors  reversed  ? 

We  can  understand  this  by  looking  at  Fig.  164.  In  one 
bow  we  cee  that  the  rays  enter  the  drops  at  the  top,  and  are 
refracted  at  the  bottom  to  the  eye  ;  in  the  other,  that  the  rays 
enter  at  the  bottom,  and  are  refracted  at  the  top  to  the  eye. 

2.  WJiy  can  we  not  see  around  a  house  or  through  a 
bent  tube ? 

The  rays  of  light  move  in  straight  lines. 

3.  What  color  would  a  painter"  use  if  he  wished  to  rep- 
resent an  opening  into  a  dark  cellar  ? 

Black. 

4.  Is  black  a  color  ? 

Np ;  it  is  the  absence  of  light,  and  hence  of  color. 
Is  white  ? 

No.  It  is  the  result  of  mixing  a  multitude  of  tints,  each  of 
which  loses  its  individuality  as  color  by  union  with  the  rest. 

5.  By  holding  an  object  nearer  a  light,  ivill  it  increase 
or  diminish  the  size  of  the  shadow  ? 

It  will  increase  it,  because  more  rays  are  intercepted. 

7.  Where  should  ^ve  look  for  a  rainboiv  in  the  morn- 
ing ? 

In  the  west. 

<V.  Can  two  spectators  see  the  same  rainboiv  ? 

They  can  not,  because  no  two  persons  can  be  at  the  right 
angle  to  get  the  same  color  from  a  drop. 

9.  Wliy,  tvhen  the  drops  of  ivater  are  falling  through 
the  air9  docs  the  bow  appear  stationary  ? 

Because  amid  the  multitude  of  drops  there  are  always  some 
in  the  right  direction. 

10.  Why  can  a  cat  see  in  the  night  better  than  a  human 
being  ? 


IN  POPULAR    PHYSICS.  43 

Because  the  pupils  of  its  eyes  are  larger,  and  so  admit  more 

light. 

11.  Why  can  not  an  owl  see  distinctly  in  daylight  ? 

Its  eyes  are  adapted  to  faint  light.  That  of  bright  sunshine 
is  therefore  too  dazzling. 

12.  Why  are  we  blinded  tvhen  we  pass  quickly  from  a 
dark  into  a  brilliantly  lighted  room  ? 

The  pupils  of  our  eyes  admit  too  much  light,  but  they  soon 
contract  to  the  proper  dimensions,  and  we  can  then  see  dis- 
tinctly. When  we  pass  out  from  a  lighted  room  into  a  dark 
room,  the  conditions  are  reversed. 

13.  If  the  light   on  a  distant  planet  is  only  ^  that 
which  ive  receive,  how  does  its  distance  from  the  sun  com- 
pare ivith  ours  ? 

As  the  intensity  of  light  is  inversely  as  the  square  of  the 
distance,  the  distance  is  ^,/100  =  10  times  as  great  as  ours. 

14.  If  ivhen  I  sit  6  feet  from  a  candle  I  receive  a  cer- 
tain amount  of  light,  hoiv  much  ivill  I  diminish  it  if  I  sit 
back  6  feet  farther  ? 

As  my  distance  from  the  light  is  doubled,  the  brightness  is 
inversely  as  22,  or  only  £  as  great. 

15.  Why  do  drops  of  rain,  in  falling,  appear  like  liquid 
threads  ? 

The  impression  the  drop  makes  on  the  retina  remains  until 
the  drop  reaches  the  ground. 

16.  W7iy  does  a  towel  turn  darker  when  wet  ? 

More  of  the  light  is  transmitted,  and  less  reflected.  "We  see 
this  illustrated  in  greasing  a  bit  of  paper.  It  becomes  semi- 
transparent  because  more  light  passes  through  it,  but  looks 
darker  itself  because  less  light  is  reflected  to  the  eye. 

17.  Does  color  exist  in  the  object  or  in  the  mind  of  the 
observer ? 


44  ANSWERS    TO    PRACTICAL     QUESTIONS 

The  property  of  absorbing  energy  of  special  wave  length, 
and  reflecting  that  of  another  wave  length  which  we  perceive 
as  color,  is  a  physical  property  of  the  object.  The  perception 
of  this,  as  of  sound,  or  of  temperature,  is  finally  a  mental  act. 

18.  IVTiy  is  lather  opaque,  while  air  and  a  solution  of 
soap  are  each  transparent  ? 

By  repeated  reflections  and  refractions  in  passing  through 
the  mass  of  lather,  no  ray  can  pass  through  in  a  straight  line. 
Transparency  is  hence  destroyed. 

19.  Why  does  it  ivhiten  molasses  candy  to  pull  it  ? 

The  viscous  mass,  by  repeated  pulling,  becomes  fibrous.  The 
fibers  at  the  surface  reflect  light  more  regularly,  and  hence  the 
candy  appears  more  nearly  white. 

20.  Why  does  plastering  become  lighter  in  color  as  it 
dries  ? 

Because,  as  the  water  evaporates,  the  mortar  transmits  less 
light,  and  reflects  more  light  to  the  eye. 

21.  Why   does  the  photographer  use  a  lamp  ivith  a 
chimney  of  red  glass  in  the  "  dark  room  "  ? 

Because  this  glass  transmits  only  the  longer  waves  of  light, 
while  chemical  effect  is  produced  chiefly  by  the  shorter  waves. 

22.  Is  the  common  division  of  colors  into  "  cold  "  and 
"  warm  "  verified  in  philosophy  ? 

Yes  ;  red  contains  more  heat  than  violet. 

23.  Why  is   the  image  on  the  camera,   Fig.  177,  in- 
verted ? 

The  rays  cross  each  other  at  the  focus  of  the  double  convex 
lens. 


24.  Wliy  is  the  second  image  seen  in  the  mirror9 
14O,  brighter  than  the  first? 

The  first  is  formed  by  reflection  from  the  glass,  and  the 
second  from  the  mercury.  As  the  latter  is  a  better  reflector, 
the  second  image  will  be  brighter.  Each  image  after  that  will 
be  weakened  by  the  repeated  reflection. 


IN   POPULAR    PHYSICS.  45 

27.  Which  will  be  seen  at  the  greater  distance ,  a  yellow 
or  a  gray  body  ? 

The  yellow,  since  it  is  brighter. 

28.  IVlien  a  star  is  near  the  horizon,  does  it  seem  higher 
or  lower  than  its  true  place  ? 

Higher.  The  light  in  passing  into  our  atmosphere,  is  re- 
fracted downward,  and  the  star  appears  in  the  direction  from 
which  the  ray  enters  the  observer's  eye. 

29.  Why  can  we  not  see  a  rainbow  at  midday  ? 

Because  the  sun  is  not  in  the  right  position.  To  produce 
the  ordinary  rainbow,  it  must  be  toward  the  eastern  or  western 
horizon. 

30.  What  conclusion  do  we  draiv  from  the  fact  that 
moonlight  shows  the  same  dark  lines  as  sunlight  ? 

That  its  light  has  the  same  source  as  that  of  the  sun,  and 
is,  indeed,  reflected  sunlight. 

31.  IFliy  does  the  bottom  of  a  boat  seen  under  clear 
ivater  appear  flatter  than  it  really  is  ? 

Because,  by  refraction,  the  bottom  of  the  boat  is  apparently 
elevated  above  its  true  place. 

32.  Of  what    shape    docs   a  round    body   appear    in 
^vater  ? 

It  appears  to  be  flattened ;  and  hence  a  round  body  looks 
like  an  oval  one. 

33.  Why  is  rough  glass  translucent  while  smooth  glass 
is  transparent  ? 

The  minute  irregularities  scatter  the  rays  of  light,  and  do 
not  allow  them  to  pass  freely  to  the  eye  of  the  observer. 

34.  Why  can  a  carpenter  looking  along  the  edge  of  a 
board  tell  ivhether  it  is  straight  ? 

If  the  edge  is  straight,  the  light  will  be  reflected  uniformly 
to  his  eye  from  the  whole  length.  Any  uneven  places  will  make 
dark  and  light  spots. 


46  ANSWERS    TO    PRACTICAL     QUESTIONS 

35.  Why  can  ^ve  not  see  out  of  the  windoiv  after  ive 
have  lighted  the  lamp  in  the  evening  ? 

The  glass  reflects  the  light  of  the  lamp  back  to  our  eyes, 
and  they  adapt  themselves  to  the  increased  amount. 

36.  Why  does  a  ground-glass  globe  soften  the  light  ? 

It  scatters  the  rays. 

37.  Why  can    we    not   see    through    ground-glass    01* 
painted  windows  ? 

They  transmit  the  light  irregularly  to  the  eye,  and  not  uni- 
formly, like  a  transparent  body. 

38.  Why  does  the  moon's  surface  appear  flat? 

Because  it  is  so  distant  that  the  eye  can  not  detect  the  dif- 
ference between  the  distance  of  the  center  and  the  circumfer- 
ence. 

39.  Why  can  ^ve  see  farther  with  a  telescope  than  ivith 
the  naked  eye  ? 

Because  it  furnishes  us  more  light  with  which  to  see  a  dis- 
tant object. 

40.  Why  is  not  snow  transparent,  liJte  ice  ? 

Because  it  is  discontinuous,  and  the  rays  of  light  are  broken 
by  multitudinous  reflections  and  refractions. 

4:1.  Are  there  rays  in  the  sunbeam  which  we  can  not 
see? 

We  can  not  see  the  heat  or  the  chemical  rays. 

42.  Why,  when  we  press  the  finger  on  one  eyeball,  do 
we  see  objects  double  ? 

Because  the  rays  from  the  same  external  object  fall  on  parts 
of  the  two  retinas  that  do  not  correspond  in  position. 

43.  Why  does  a  distant  light,  in  the  night,  seem  like  a 
star  ? 

Because  its  image  on  the  retina  is  so  small  that  deception 
becomes  easy. 


IN   POPULAR    PHYSICS.  47 

44:.  Why  does  a  bright  light,  in  the  night,  seem  so  much 
nearer  than  it  is  ? 

We  judge  of  the  distance  of  an  object  by  its  magnitude,  by 
its  distinctness  of  outline,  and  by  the  size,  etc.,  of  intervening 
objects  with  which  we  compare  it.  In  the  night,  the  Ixrightness 
of  a  light  confuses  us  by  its  vividness,  seeming  to  be  near  at 
hand.  Moreover,  we  can  not  see  the  neighboring  objects,  whose 
distance  we  know  or  could  estimate  in  the  daylight.  Our  error 
is  therefore  one  of  judgment. 

45.  What  color  predominates  in  artificial  lights  ? 

Yellow. 

46.  Why  are   we   not  sensible   of  darkness  when  we 
wink  ? 

Because  the  wink  does  not  last  so  long  as  the  impression  of 
the  light  received  just  before  the  wink. 

47.  Under  ivhat  condition  do  the  eyes  of  a  portrait 
seem  to  follow  a  spectator  to  all  parts  of  a  room  ? 

This  is  noticed  only  in  a  full-face  portrait.  In  that  case  the 
spectator,  when  he  goes  to  either  side,  fails  to  see  the  side  of 
the  eyeballs,  and  hence  the  effect  is  that  of  looking  directly  into 
the  eye.  "A  rifleman,  portrayed  as  if  taking  aim  directly  in 
front  of  the  picture,  appears  to  every  observer  to  be  pointing 
at  him  specially." 

48.  Why  do  the  two  parallel  tracks  of  a  railroad  ap- 
pear to  approach  in  the  distance  ? 

The  visual  angle  subtended  by  the  distance  between  two  op- 
posite points  on  the  tracks  becomes  less  as  the  distance  of  the 
observer  increases. 

49.  W7iy  does  a  fog  apparently  magnify  objects  ? 

It  is  not  the  refraction  of  the  rays  of  light,  as  is  commonly 
supposed,  which  makes  an  object  seem  larger  when  seen  through 
a  mist.  It  really  appears  to  us  in  its  proper  size.  The  mist, 
however,  dims  the  color  and  the  outline,  giving  it  the  indis- 
tinctness belonging  to  a  mile  in  distance,  while  it  has  the  mag- 
nitude of  half  a  mile.  Dr.  "Wayland  relates  that,  as  he  was 


48  ANSWERS    TO    PRACTICAL     QUESTIONS 

sailing  through  Newport  harbor  early  one  morning,  in  a  dense 
fog,  he  observed  on  the  apparently  distant  wharf  some  very  tall 
men.  While  he  was  remarking  upon  their  extraordinary  size, 
he  was  astonished  to  see  them  jumping  about  like  children,  and 
otherwise  behaving  in  a  most  unaccountable  manner.  Pres- 
ently, as  the  sun  dispersed  the  fog,  he  found  that  he  was  closo 
to  the  wharf,  and  that  the  gigantic  men  were  really  a  party  of 
small  boys  amusing  themselves  with  play. 

The  opposite  mistake  is  made  when  the  atmosphere  is  more 
transparent  than  that  to  which  we  are  accustomed.  Foreign 
travelers  in  Switzerland,  who  have  started  on  foot  to  visit  a 
glacier  or  a  mountain-peak  which  seemed  within  easy  distance, 
have  often  been  surprised  to  find,  after  two  or  three  hours  of 
brisk  walking,  that  the  object  of  their  desire  seemed  as  far 
away  as  at  first.  So  in  looking  across  a  sheet  of  water,  where 
there  are  no  intervening  objects,  distance  is  always  underrated. 

When  we  throw  a  stone  at  an  object  in  the  water  we  find 
that  our  eye  has  deceived  us,  and  the  stone  falls  far  short  of 
the  mark.  For  the  same  reason,  objects  seen  on  the  shore  from 
the  water  seem  much  less  than  their  natural  size.  The  fact  is, 
they  appear  of  the  magnitude  which  belongs  to  the  distance, 
but  we  suppose  the  distance  less  than  it  is ;  and,  associating 
tnis  magnitude  with  diminished  distance,  they  appear  to  us  less 
than  they  really  are. 

In  order  to  form  these  judgments  correctly,  one  of  these 
elements  must  be  fixed.  From  this  we  learn  to  institute  a  com- 
parison, and  thus  form  an  accurate  opinion.  If  we  know  the 
magnitude  of  an  object,  the  change  in  its  color  and  outline  will 
teach  us  its  distance.  If  we  know  its  distance,  we  can  judge  of 
its  magnitude.  Hence,  painters,  in  order  to  give  us  a  correct 
idea  of  an  object  which  they  represent,  always  place  in  its 
vicinity  something  with  whose  real  magnitude  we  are  familiar. 
Thus,  to  show  the  size  of  a  pyramid,  an  Arab  with  his  camel 
may  be  drawn  at  its  foot.  If  the  pyramid  were  represented  by 
itself,  its  intended  size  might  be  mistaken  ;  but  every  one  knows 
the  size  of  a  camel,  and  from  this  he  would  judge  of  the  mag- 
nitude of  a  pyramid. —  Wayland's  Intellectual  Philosophy,  p.  78, 
et  seq. 


IN   POPULAR    PHYSICS.  49 

50.  If  yon  sit  where  you  can  not  see  another  person's 
image,  why  can  not  that  person  see  yours  ? 

The  angle  of  incidence  is  equal  to  the  angle  of  reflection 
under  all  circumstances.  If  a  ray  from  the  other  person  is  not 
reflected  at  the  right  angle  to  reach  your  eye,  then  a  ray  from 
you  is  not  reflected  at  the  right  angle  to  reach  the  other  per- 
son's eye. 

51.  IVliy  can  we  see  the  multiple  images  in  a  mirror 
better  if  we  look  into  it  very  obliquely  ? 

More  light  is  then  reflected  to  the  eye.  The  ratio  of  the 
light  reflected  to  the  light  refracted  increases  with  the  angle  of 
incidence. 

52.  Why  is  an  image  seen  in  water  inverted  ? 

(Examine  Fig.  139  in  Physics.) 

53.  Why  is  the  sun's  light  fainter  at  sunset  than  at 
midday ? 

(See  Physics,  p.  191,  note.) 

54.  WJty  can  we  not  see  the  fence-posts  ^vhen  we  are 
riding  rapidly  ? 

Because  the  images  of  a  succession  of  objects  are  formed 
on  the  retina  at  intervals  less  than  that  of  the  duration  of  a 
retinal  impression.  Hence,  they  all  become  confused,  and  noth- 
ing is  seen  distinctly. 

55.  Ought  a  red  flower  to  be  placed  in  a  bouquet  by  an 
orange  one  ?    A  pink  or  blue  with  a  violet  one  ? 

(Seo  Physics,  p.  217.) 

These  are  not  complementary  colors,  and  hence  do  not 
strengthen  each  other  by  contrast. 

56.  IVJiy  are  the  clouds  ^vhite  while  the  clear  sky  is 
blue? 

Prof.  Tyndall  has  shown  that  the  larger  particles  of  vapor 
scatter  light  of  all  colors,  i.e.,  white  light;  while  the  smallest 
particles,  only  the  blue  rays.  In  accordance  with  this  fact,  the 
clouds  are  white  and  the  sky  is  blue.  If  the  air  were  abso- 
lutely pure,  free  from  all  foreign  matter,  and  highly  rarefied, 


50  ANSWERS    TO    PRACTICAL     QUESTIONS 

it  is  thought  that  the  azure  of  the  sky  would  not  be  seen,  and 
the  heavens  would  appear  black  :  the  illumination  of  objects 
would  be  strong  and  glaring  on  one  side,  and  on  the  opposite 
side  the  shadows  would  be  deep  and  unrelieved  by  the  diffused 
light  to  which  we  are  accustomed.  The  minute  particles  of  va-  » 
por  in  the  air  serve  to  scatter  the  direct  rays  of  the  sun,  and  to 
turn  them  around  corners  and  into  places  not  in  the  direct  line 
of  the  sunlight. 

(See  a  full  and  interesting  discussion  in  Tyndall's  Lecture  on  Light,  p. 
152,  et  seq,) 

57.  IVliy    does    skim -milk   look  blue    and   neiv  milk 
white  ? 

The  fatty  globules  of  the  new  milk  reflect  all  the  colors  of 
the  spectrum  to  the  eye ;  but  when  deprived  of  the  cream  the 
milk  reflects  the  blue  light  in  excess  of  the  others. 

58.  Why  is  not  the  image  of  the  sun  in  water  at  mia^ 
day  so  bright  as  near  sunset  ? 

The  angle  of  incidence  being  small,  most  of  the  light  is 
transmitted,  and  but  little  is  reflected.  Near  sunset  the  greater 
part  is  reflected. 

59.  Why  is  the  rainboiv  always  opposite  the  sun  ? 

(See  Physics,  p.  217.) 

60.  Sold  a  card  with  its  edge  close  in  front  of  your  eye 
and  look  at  a  distant  candle  flame  in  a  dark  room.     You 
will  probably  perceive  either  a  reddish  or  a  bluish  fringe 
on  one  side.    Explain. 

The  crystalline  lens  is  not  corrected  for  chromatic  aberra- 
tion. (See  Physics,  p.  219.) 

HEAT. 

273— 1.  Wtiy  will  one's  hand,  on  a  frosty  morning, 
freeze  to  a  metallic  door-knob  sooner  than  to  one  of  porce- 
lain ? 

Because  the  metal  is   a  better  conductor   of   heat   than  the 
porcelain,  and  hence  conducts  the  heat  from  the  hand  faster. 


IN   POPULAR    PHYSICS.  51 

2.  Why  does  a  piece  of  bread  toasting  curl  up  on  the 
side  toward  the  fire  ? 

The  v/ater  being  expelled  from  the  pores  on  that  side  causes 

tho  bread  to  shrink. 

3.  Wluj  do  double  ivindoivs  protect  from  the  cold  ? 

The  non-conducting  air  inclosed  between  the  window-panes 
keeps  in  the  heat  and  keeps  out  the  cold. 

4.  Why  do  furnace-men  wear  flannel  shirts  in  summer 
to  keep  cool,  and  in  ivinter  to  keep  warm,  ? 

In  summer  the  non-conducting  flannel  keeps  out  the  fur- 
nace-heat, and  in  the  winter  keeps  in  the  body-heat. 

5.  Why  do  ^ve  blow  our  hands  to  make  them  warm, 
and  out-  soup  to  make  it  cool  ? 

Our  breath  is  warmer  than  our  hands,  but  cooler  than  our 
soup. 

6.  Why  does  snow  protect  the  grass  in  winter  ? 

The  air  inclosed  between  the  flakes  of  snow  is  a  non-con- 
ductor. No  infant  in  its  cradle  is  tucked  in  more  tenderly  than 
the  coverlet  of  snow  about  the  humble  grass  that  nestles  down 
for  its  winter's  nap  on  the  bosom  of  Mother  Earth. 

7.  Why   does  water   "boil  away"   more    rapidly   on 
some  days  than  on  others? 

Because  the  atmospheric  pressure  varies,  independently  of 
the  fact  that  the  source  of  heat  may  vary  without  our  noticing  it. 

8.  What  causes  the  crackling  sound  in  a  stove  ^vhen  a 

fire  is  lighted  ? 

Tho  expansion  of  the  iron  by  the  heat. 

,9.  TTh ?/•/.«?  the  tone  of  a  piano  higher  in  a  cold  room 
than  in  a  warm  one? 

The  steel  wires  lengthen  in  a  warm  room,  and  so  lower  the 
tone. 


52  ANSWERS    TO    PRACTICAL    QUESTIONS 

10.  Ought  an   inkstand  to  have  a  large  or   a  small 
mouth  ? 

A  small  mouth,  to  prevent  evaporation. 

11.  Why  is  there  a  space  left  between  the  ends  of  the 
rails  on  a  railroad  trade  ? 

To  allow  room  for  the  expansion  and  contraction  of  the 
rails  with  the  changes  in  temperature. 

12.  Why  is  a  person  liable  to  take  cold  when  Jiis  clothes 
are  damp? 

The  water  which  evaporates  from  his  clothes,  in  drying,  ab- 
sorbs heat  from  his  body. 

13.  What  is  the  theory  of  corn-popping  ? 

The  air  in  the  cells  of  the  corn  expands  by  the  heat,  and 
bursts  the  outer  coating  of  the  corn. 

14.  Could  vacuum-pans  be  employed  in  cooking  ? 

They  could  not,  because  the  heat  would  not  be  sufficient  to 
cook  the  food. 

15.  Why  does  the  air  feel  so  chilly,  in  the  spring,  ivhen 
snow  and  ice  are  melting  ? 

When  the  ice  is  passing  into  the  liquid  state,  it  absorbs  heat 
from  all  surrounding  objects. 

1(>.  Why,  in  freezing  ice-cream,  do  we  put  the  ice  in  a 
ivooden  vessel,  and  the  cream  in  a  tin  one  ? 

The  non-conducting  wooden  vessel  prevents  the  ice  from  ab- 
sorbing heat  from  the  external  air,  and  the  conducting  tin  ves- 
sel enables  it  to  absorb  the  heat  from  the  cream. 

17.  Wliy  does  the  temperature  generally  moderate 
when  the  snoiv  falls  ? 

The  vapor  passing  into  the  solid  form  gives  off  heat. 

19.  Why  does  sprinkling  a  floor  ivith  ivater  cool  the 
air? 

The  water  turning  to  vapor  absorbs  heat. 


IN   POPULAR    PHYSICS.  53 

20.  How  low  a  degree  of  temperature  can  be  reached 
with  a  mercurial  thermometer  ? 

Nearly  to  the  freezing  point  of  mercury,— 39°  F. 

21.  If  the  temperature  be  7O°  F.,  ivhat  is  it  C.  ? 

70° -32°  =  38°.     38-^1.8  =  21.1°  C. 
If  the  temperature  be  7O°  C.,  what  is  it  F.  ? 
70°  x  1.8  =  126°.     126° +  32°  =  158°  F. 

22.  Will  dew  form  on  an  iron  bridge  ? 
Yes,  because  iron  is  a  good  radiator. 

On  a  planJt  walk  ? 

Not  so  readily,  because  wood  is  a  poorer  radiator. 

23.  Why  will  not  corn  pop  when  very  dry  ? 

The  pores  shrink,  and  the  corn  becomes  compact ;  only  por- 
ous, tender-celled  corn  will  pop. 

24.  When  the  interior  of  the  earth  is  so  hot,  why  do  we 
get  the  coldest  water  from  a  deep  well? 

The  well  extends  below  the  influence  of  the  sun,  and  not 
deep  enough  to  be  affected  by  the  internal  heat  of  the  earth. 

25.  Ought  the  bottom  of  a  tea-Kettle  to  be  polished  ? 

No,  since  a  polished  surface  would  reflect  the  heat.  We 
need  a  black,  rough,  sooty  surface  to  absorb  the  heat  rapidly. 

26.  Which  boils  the  sooner,  milk  or  water  ? 

Milk,  because  it  is  so  adhesive  that  the  bubbles  of  steam 
which  are  formed  at  the  bottom  of  the  dish  can  not  easily  es- 
cape. They  therefore  pile  up  on  top  of  each  other,  and  the 
milk  boils  over  readily. 

27.  Is  it  economy  to  keep  our  stoves  highly  polished? 

The  stove-blacking  used  is  a  good  radiator,  but  the  surface 
should  not  be  highly  polished,  as  that  hinders  radiation. 

28.  If  a  thermometer  be  held  in  a  running  stream,  will 
it  indicate  the  same  temperature  that  it  would  in  a  pailful 
of  the  same  ivater  ? 


54  ANSWERS    TO    PRACTICAL     QUESTIONS 

It  will.  For  the  same  reason  that  a  thermometer,  in  the 
wind,  will  indicate  the  same  temperature  as  in  the  still  air,  al- 
though the  former  seems  to  us  much  colder. 

29.  Which  makes  the  better  holder  when  one  wishes  to 
protect  his  hands  from  a  hot  dish,  woolen  or  cotton  ? 

Woolen,  because  it  is  so  poor  a  conductor  of  heat. 

30.  Which  ivill  give  out  the  more  heat,  a  plain  stove  or 
one  with  ornamental  designs  ? 

The  latter,  since  it  has  more  radiating  surface. 

31.  Does  dew  fall? 

No;  it  forms  directly  where  it  is  found.  The  vapor  merely 
collects  on  the  cold  surface. 

32.  What  causes  the  "  sweating  "  of  a  pitcher  ? 

The  vapor  of  the  air  condenses  on  the  cold  pitcher.  It  is 
often  a  sign  of  rain,  since  it  shows  that  the  air  is  full  of  vapor 
easily  deposited. 

33.  Why  is  evaporation  hastened  in  a  vacuum  ? 

Because  the  pressure  of  the  air  is  removed. 

34.  Does  stirring  the  ground  around  plants  aid  in  the 
deposition  of  dew  ? 

It  does,  since  it  facilitates  radiation. 

35.  Wliy  does  the  snow  at  the  foot  of  a  tree  melt  sooner 
than  that  in  the  open  field  ? 

The  tree  absorbs  the  sun's  heat,  and  then  radiates  it  out, 
thus  serving  as  a  carrier  for  the  snow. 

36.  WJty  is  the  opening  in  a  chimney  made  to  decrease 
in  size  from  bottom  to  top  ? 

Because  as  the  heated  air  rises  it  cools  and  shrinks.  If 
the  chimney  did  not  diminish  in  size  correspondingly,  currents 
of  cold  air  would  set  down  from  the  top. 

37.  Will  tea  keep  hot  longer  in  a  bright  or  in  a  dull 
tea-pot  ? 


J.V    POPULAR    PHYSICS.  55 

In  a  bright  one,  since  a  polished  surface  retards  radiation. 

38.  JJJiat  causes  the  snapping  of  wood  when  laid  on 
the  fire? 

The  expansion  of  the  air  in  the  cells  of  the  wood. 

39.  Why  is  one's  breath  visible  on  a  cold  day  ? 

The  vapor  in  the  breath  is  condensed  by  the  cold  air. 

40.  What  gives  tlie  blue  color  to  air  ? 

The  particles  floating  in  it  reflect  the  blue  light  of  the  sun- 
beam. 

4:1.  How  does  the  heat  at  two  feet  from  the  fire  compare 
with  that  at  four  feet? 

2*  ;  42 ; :  1  :  4. 
Hence  it  is  four  times  greater. 

4=2.  Why  does  the  frost  remain  later  in  the  morning 
upon  some  objects  than  upon  others  ? 

The  best  radiators  are  the  best  absorbers.  They  become 
warmed  by  the  morning  sun  more  quickly  than  the  poorer 
radiators,  and  the  frost  on  them  is  hence  more  quickly  melted. 

43.  Is  it  economy  to  use  green  ivood  ? 

No.  Its  sap  has  to  be  changed  to  vapor,  thus  absorbing  a 
large  amount  of  energy  at  the  expense  of  the  combustion. 

44.  Why  does  not  green  wood  snap  ? 

The  pores  are  filled  with  water  instead  of  air.  The  water 
does  not  expand  rapidly  enough  to  burst  off  the  coverings  of 
the  cells,  and  so  simply  oozes  out  gradually,  and  is  vaporized. 

45.  Wliy  will  a  piece  of  metal  dropped  into  a  glass  or 
porcelain  dish  of  boiling  ivater  facilitate  the  ebullition  ? 

The  rougher  surface  of  the  metal  aids  in  the  formation 
and  disentanglement  of  the  steam-bubbles.  The  bubbles  cling 
longer  to  a  smooth  than  to  a  rough  surface.  This  is  one 
cause  of  that  bumping  sound  often  noticed  when  liquids  are 
boiling  in  glass  dishes. 


56  ANSWERS    TO    PRACTICAL     QUESTIONS 

46.  Which  can  be  ignited  the  more  easily  'with  a  burn- 
ing-glass, black  or  white  paper  ? 

Black  paper,  since  it  is  a  much  better  absorber  of  heat. 

47.  Why  does  the  air  feel  colder  on  a  windy  day  ? 

Because  fresh  portions  of  cold  air  are  brought  constantly  in 
contact  with  our  bodies. 

48.  Could  a  burning-lens  be  made  of  ice  ? 

Burning-lenses  have  been  made  of  that  material.  The  rays 
have  no  heating  power  until  the  waves  of  ether  are  stopped. 
They  do  not  elevate  the  temperature  of  the  medium  through, 
which  they  pass. 

49.  IVhy  is  an  iceberg  frequently  enveloped  by  a  fog  ? 

The  moisture  of  the  air  is  condensed  upon  its  cold  surface. 

50.  Would  dew  gather  more  freely  on  a  rusty  stove 
than  on  a  bright  Kettle  ? 

It  would,  because  the  rusty  iron  surface  is  a  good  radiator. 

51.  Why  is  a  clear  night  colder  than  a  cloudy  one  dur- 
ing the  same  season  ? 

On  a  cloudy  night  the  clouds  reflect  the  radiated  heat  of  the 
earth  back  again,  and  thus  act  as  a  blanket  to  keep  the  earth 
warm.  On  such  a  night  there  can  be  no  frost  or  dew.  On  a 
clear  night,  the  heat  which  the  earth  radiates  passes  out  freely 
into  space,  and  thus  the  earth  cools  rapidly. 

52.  Why  is  no  dew  formed  on  cloudy  nights  ? 

See  last  question. 

53.  Why  will  "fanning  "  cool  the  face  ? 

It  brings  in  contact  with  the  face  a  current  of  fresh  and 
generally  cooler  air. 

54.  How  are  safes  made  fire-proof? 

By  filling  the  space  between  the  inner  and  the  outer  iron 
plates  with  a  non-conducting  material,  as  plaster,  etc.,  the  safe 
is  rendered  nearly  fire-proof. 


IN   POPULAR    PHYSICS.  57 

55.  Why  can  you  heat  water  quicker  in  a  tin  than  a 
china  cup  ? 

Because  the  metal  is  a  better  conductor  of  heat  than  the 
china. 

56.  WJiy  will  a  woolen  blanket  keep  ice  from  melting  ? 

The  woolen  is  a  non-conductor  of  heat. 

57.  Does  dew  form  under  trees  ? 

The  trees  reflect  back  the  heat  radiated  by  the  earth,  grass, 
etc.,  and  so  prevent  the  temperature,  in  general,  from  sinking 
to  the  dew-point. 

58.  Wliat  is  the  principle  of  heating  by  steam  ? 

The  steam  is  condensed  in  the  pipes,  and  gives  out  as  tem- 
perature the  energy  which  had  been  previously  absorbed  in 
changing  water  to  steam. 

59.  IFJiat  is  the  cause  of  "  cloud-capped  "  mountains  ? 

The  warm,  moist  air  from  the  valleys  rises  against  the 
mountain  sides.  Its  vapor,  previously  invisible,  becomes  con- 
densed by  the  colder  air  into  a  cloud  of  droplets  that  float  in 
the  air. 

60.  Show  how  the  glass  in  a  hot-house  acts  as  a  trap  to 

catch  the  sunbeam. 

(See  Physics,  p.  259.) 

61.  Does  the  heat  of  the  sun  come  in  through  our  ivin- 

doivs  ? 

(See  Physics,  p.  259.) 

62.  Does  the  heat  of  our  stoves  pass  out  in  the  same 

tvay  ? 

(See  Physics,  p.  259.) 

63.  TJie  top  of  a  mountain  is  nearer  the  sun;  why  is  it 

not  ivarmer  ? 

(See  Physics,  pp.  250  and  200.) 

67.  Can  we  find  frost  on  the  ivindows  and  on  the  stone- 
flagging  the  same  morning  ? 

It  requires  a  much  intenser  cold  to  produce  the  former  ef- 
fect than  the  latter,  as  glass  is  a  poorer  conductor  of  heat  than 


58  ANSWERS    TO    PRACTICAL     QUESTIONS 

stone.  We  frequently  find  frost  on  the  nagging  early  in  the 
fall,  but  frost  on  the  window  is  a  sign  of  very  severe  winter 
weather. 

68.  IFhy  will  not  snow  "pack"  into  balls  except  in 
mild  weather  ? 

The  snow  must  be  very  near  the  melting-point  for  the  press- 
ure of  the  hand  to  be  sufficient  to  melt  enough  of  it  to  pro- 
duce the  phenomena  of  regelation.  (Physics,  p.  271,  1st  note ; 
also  Tait's  Recent  Advances  in  Physical  Science,  p.  129,  and 
Tyndall's  Forms  of  Water,  p.  163.)  This  principle  involves  the 
theory  of  Glaciers.  "  The  masses  of  snow  can  not  rest  on  the 
steep  slopes  of  Alpine  summits.  The  pressure  upon  the  under 
layers  is  too  great  to  allow  them  to  remain  upon  their  sloping 
beds,  and  they  are  forced  to  descend.  This  descent  is  accom- 
plished in  two  forms :  that  of  an  avalanche,  one  of  the  most 
awful  and  imposing  spectacles  to  witness ;  or  of  a  glacier, 
which  is  really  an  avalanche  of  ice  of  extremely  slow  motion. 
But  the  glacier  differs  from  the  ordinary  avalanche  not  only  in 
that  its  motion  is  so  slow,  but  in  that  it  consists  of  ice,  thick, 
firm,  and  hard.  The  principles  involved  in  this  transition  of 
the  loose,  flaky  snow  which  first  falls  upon  the  mountain-top 
into  the  solid  ice  of  the  glacier,  are  very  well  illustrated,  as 
Helmholtz  has  remarked,  in  the  manufacture  of  the  school- 
boy's snow-ball  or  snow-man.  Very  cold  snow  is  always  light 
and  flaky,  and  can  not  be  made  by  the  pressure  of  the  hands 
into  a  cohesive  mass  ;  in  order  to  succeed  in  that  operation, 
snow  is  always  employed  which  is  already  at  the  melting-point, 
or  only  so  far  below  this  temperature  that  the  warmth  of  the 
hand  suffices  to  bring  it  to  the  required  temperature,  and  then, 
by  dint  of  pressure  and  molding,  an  icy  ball  may  be  easily 
produced.  So  with  the  formation  of  the  glacier  ice.  A  process 
of  almost  simultaneous  melting  and  freezing  goes  on  among 
the  under  layers  of  snow,  and  under  an  immense  and  ever- 
constant  pressure  from  the  weight  of  the  snow  above  ;  thus 
solid  ice  is  formed.  That  this  ice  conforms  itself  to  the  various 
windings,  constrictions,  and  dilatations  of  its  rocky  channel 
during  its  downward  march,  is  a  fact  not  less  familiar  than 
wonderful." 


IN    POPULAR    PHYSICS.  59 

69.  WJiy  is  the  sheet  of  zinc  under  a  stove  so  apt  to  be- 
come puckered  ? 

When  zinc  cools  after  expansion  it  does  not  return  quite  to 
its  former  dimensions,  and  so  becomes  "  puckered,"  as  it  is 
called. 

70.  WJiy  does  a  mist  gather  in  the  receiver  of  the  air- 
pump  as  the  air  becomes  rarefied  ? 

"The  remaining  air,  cooled  by  rarefaction,  absorbs  heat 
from  the  invisible  vapor  in  combination  with  it,  and  renders 
the  water  visible.  The  mist  may  be  removed  by  continued  ac- 
tion of  the  machine,  or  by  re-admitting  the  normal  quantity  of 
air." 

(See  Arnott's  Physics,  p.  448.) 

71.  Why  are  the  tops  of  high  mountains  in  the  tropics 
covered  ivith  perpetual  snow  ? 

See  question  59. 


MISCELLANEOUS    QUESTIONS   AND 
PROBLEMS    FOE    REVIEW. 

1.  Does  a  plumb  -  line  point  to  the  earth's  center  of 
figure  or  center  of  gravity  ? 

2.  In  a  dark  room,  let  the  light  of  a  candle  pass  through 
a  small  hole  in  a  card,  and  the  image  of  the  candle  on  the 
opposite  wall  will  be  inverted.    Explain. 

3.  How  many  titties  heavier  is  the  earth  than  an  equally 
large  globe  of  water? 

4:.   Why  does  a  rocket  ascend  into  the  air  ? 

5.  Is  the  water  at  the  foot  of  Niagara  Falls  warmer 
than  that  in  the  river  above  ? 

f>.   What  causes  wheel  fire-works  to  rotate  ? 

7.  A  brass  rod  covered  tightly  with  thin  paper  may  be 
held  some  time  in  a  flame  ivithout  the  paper  being  scorched; 
while,  if  the  rod  be  of  wood,  the  paper  will  scorch  at  once. 
Wliy  is  this  difference? 


60  MISCELLANEOUS     QUESTIONS. 

8.  How  would  it  affect  the  action  of  a  siphon  if  it  ivere 
carried  up  a  mountain  ? 

9.  If  a  vessel  of  water  containing  a  floating  body  be 
placed  under  the  receiver  of  an  air-pump,  and  the  air 
gradually  exhausted,  what  will  be  the  effect  on  the  floating 
body? 

10.  How  will  it  change  the  height  of  the  column  of 
mercury  in  a  barometer  to  incline  the  tube  ? 

11.  In  the  image  of  a  written  page  seen  in  a  mirror, 
why  does  the  writing  seem  to  slope  ? 

12.  Why  does  a  coin  placed  in  a  tumbler  look  larger 
when  the  glass  is  full  of  water  than  when  it  is  empty  ? 

13.  Two  bodies  of  different  volume  iveigh  the  same  in 
water ;  which  will  weigh  the  more  in  mercury,  the  larger 
or  the  smaller  ? 

14:.  How  does  the  wind  drift  sand,  snow,  etc.  ? 

15.  Why  does  oil  " still  troubled  waters"  ? 

16.  Why  does  crouching  down  at  the  highest  points  in 
a  swing,  and  standing  up  at  the  lowest  point,  increase  the 
velocity  ? 

17 •  What  difference  would  it  make  in  the  guinea-and- 
feather  experiment  to  force  into  the  tube  additional  air, 
instead  of  exhausting  it,  as  ordinarily  done  ? 


ANSWERS 

TO    THE 

PRACTICAL  QUESTIONS  AND  PROBLEMS 

IN 

STEELE'S  POPULAR  CHEMISTRY. 

[The  large  figures  refer  to  the  page  of  the  Chemistry,  and  the  small 
ones  to  the  number  of  the  questions.] 

26 — !•  What  becomes  of  the  ivater  that  "  dries  up  "  ? 
Of  the  wood  that  "  burns  up  "  ?  Is  there  any  destruction 
of  the  matter  they  contain  ? 

The  water  is  changed  into  invisible  vapor,  and  wafted  thus 
away. 

The  wood  is  oxidized  into  CO3  and  H2O,  which  mingle  with 
the  air.  The  ashes  consist  of  SiO2,  K2CO3,  and  the  oxides  of 
any  other  elements  present  whose  compounds  with  O  are  not 
gaseous. 

There  is  no  destruction  of  the  matter  contained. 

2.  Where  is  the  higher  oxide  formed,  at  the  forge  or  in 
the  pantry  ? 

There  is  more  complete  oxidation  at  the  forge.  At  low 
temperatures,  decomposition  results  often  in  complex  products. 

3.  Wlty  is  the  blood  red  in  the  arteries,  and  darle  in  the 
veins  ? 

When  specimens  of  venous  and  of  arterial  blood  are  sub- 
jected to  chemical  examination,  the  differences  presented  by 
their  solid  and  fluid  constituents  are  found  to  be  very  small  and 
inconstant.  As  a  rule,  there  is  rather  more  water  in  arterial 
blood,  and  rather  more  fatty  matter.  But  the  gaseous  contents 
of  the  two  kinds  of  blood  differ  widely  in  the  proportion  which 


62  ANSWERS    TO    PRACTICAL     QUESTIONS 

the  carbonic  acid  gas  bears  to  the  oxygen  ;  there  being  a  smaller 
quantity  of  oxygen  and  a  greater  quantity  of  carbonic  acid,  in 
venous  than  in  arterial  blood.  And  it  may  be  experimentally 
demonstrated  that  this  difference  in  their  gaseous  contents  is 
the  only  essential  difference  between  venous  and  arterial  blood. 
For  if  arterial  blood  be  shaken  up  with  carbonic  acid,  so  as  to 
be  thoroughly  saturated  with  that  gas,  it  loses  oxygen,  gains 
carbonic  acid,  and  acquires  the  hue  and  properties  of  venous 
blood  ;  while,  if  venous  blood  be  similarly  treated  with  oxygen, 
it  gains  oxygen,  loses  carbonic  acid,  and  takes  on  the  color  and 
properties  of  arterial  blood.  —  HUXLEY'S  Lessons  in  Physiology. 

£.  Do  we  need  more  O  in  ^v^nter  than  in  summer  ? 

Yes,  if  we  are  much  exposed  to  the  open  air,  and  forced  to 
take  abundant  exercise  in  order  to  keep  warm. 

5.  Wliicli  would  starve  sooner,  a  fat  man  or  a  lean 
one  ? 

The  lean  one.  A  superabundance  of  flesh,  in  a  time  of 
scarcity,  is  taken  up  by  the  absorbents  and  thrown  into  the 
circulation,  thus  supplying  the  place  of  food  in  nourishing  the 
body. 

6.  How    do    teamsters   ^varm    themselves  by  slapping 
their  hands  together'  ? 

This  exercise  promotes  the  circulation  of  the  blood,  and  its 
oxidation  is  thus  quickened. 

7.  Could   a   person    commit    suicide    by    holding   his 
breath  ? 

Respiration  is  entirely  independent  of  consciousness,  as  is 
seen  in  sleep,  coma,  etc.  It  may  be  interrupted  for  a  few  min- 
utes, but  no  effort  of  the  will  can  enable  one  to  hold  his  breath 
until  life  is  extinct.  The  desire  for  O,  the  besoin  de  respirer,  or 
the  respiratory  sense,  as  it  is  called,  becomes  at  last  so  great 
that  the  strongest  resolution  yields  the  struggle. 


8.   Wiy  do  we  die  ivhen  our  breath  is  stopped  ? 

"  In  asphyxia  it  is  difficult  to  say  which  destroys  life,  the 
absence   of  oxygen   or  the   presence   of   carbonic  acid."  —  FLINT. 


IN    POPULAR     CHEMISTRY.  63 

There  is  an  absence  of  oxygen,  so  essential  to  every  vital 
operation,  and  also  an  accumulation  of  carbonic  acid  in  the 
system. 

0.  Wiiy  do  we  breathe  so  slowly  when  ive  sleep  ? 

The  circulation  is  less  rapid,  and  various  functions  of  the 
body  are  less  active.  There  is  hence  less  need  for  rapid  oxi- 
dation. 

10.  Hoiv  does   a  cold-blooded  animal  differ  from   a 
warm-blooded  one  ? 

In  the  imperfection  with  which  the  blood  is  oxygenated. 
The  lungs  are  often  of  small  capacity,  and  loose  texture,  and 
are  sometimes  wanting  entirely.  In  reptiles  a  portion  of  the 
blood  is  not  sent  to  the  heart,  and  hence  in  the  vessels  there  is 
a  mixture  of  arterial  and  venous  blood.  The  breathing  is  there- 
fore slow,  the  motions  are  languid,  and  there  is  little  heat. 

11.  Why  does  not  the  body  burn  otit  like  a  candle  ? 

Because  it  is  renewed  by  the  processes  of  assimilation  and 
nutrition  as  rapidly  as  it  is  destroyed  by  the  waste  of  oxida- 
tion. Whenever  the  former  are  in  excess  we  gain  flesh ;  when 
the  latter,  we  grow  poor. 

12.  Do  all  parts  of  the  body  change  alike? 

The  rate  of  change  varies  with  the  amount  of  oxidation, 
and  that  depends  on  the  use  of  the  organ.  The  right  arm  of 
the  blacksmith  must  be  transformed  much  more  rapidly  than 
the  left. 

13.  WJiat  objects  would  escape  combustion  if  the  air 
were  undiluted  O  ? 

Burnt  bodies,  i.e.,  those  which  are  already  combined  with 
oxygen. 

14.  Why  is  it  difficult  to  obtain  O  from  the  air  ? 

Because,  although  free  from  combination,  it  is  intimately 
mixed  with  N. 

15.  What  ^veight  of  O  can  be  obtained  from  1O  (/rams 
ofHgO? 


64  AtfSWEXS    TO    PRACTICAL     QUESTIONS 

HgO  :  O  :  :  10  :  jr. 
216  :  16::  10:  a:. 

16x10 

x  =     216     =.74:  +  ,  grams. 

16.  How  much  O  can  be  obtained  from  6  grains  of 
KCIO3  ? 

KC1O3  :  O3  :  :  6  :  x. 
122.5  :  48  :  :  6  :  x. 


17.  Hoiv  much  KCIOZ  would  be  needed  to  produce  2 
kilograms  of  O  ? 

03  :  KC103  :  :  2  :  x. 
48  :    122.5  :  :  2  :  x. 

122.5x2 

x  =  -  j^  -  =  5.1  +  ,  kilograms. 

18.  How  much  KCl  would  be  formed  in  preparing  1 
kilogram  of  O  ? 


Hence,  O3  :  KCl  :  :  1  :  x. 

48  :  74.5  :  :  1  :  x. 
74  5 
x  =  -j^-  =  1.55  +  ,  kilograms. 

19.  Is  it  probable  that  all  the  elements  fire  discovered? 

No.  But  all  new  elements  lately  discovered  have  proved  to 
be  chemical  rarities.  Probably  all  of  the  abundant  and  gener- 
ally useful  elements  have  been  discovered. 

20.  Is  heat  produced  by  oxidation  ? 

It  is  a  manifestation  of  chemical  change.  In  this  sense  it 
may  be  considered  to  be  caused  by  it. 

21.  What  is  the  difference  betiveen  kinetic  and  potential 
energy  ? 

Kinetic  energy  is  energy  of  motion  ;  potential  energy  is 
that  of  position.  (Consult  Steele's  Popular  Physics,  p.  35.) 

22.  ^Vliy  does  running  cause  pantiny  ? 


IN    POPULAR     CHEMISTRY.  65 

One  of  several  causes  is  the  need  of  more  O  to  supply  the  in- 
creased oxidation  in  the  blood  necessitated  by  unusual  exertion. 

23.  How  does  O  give  us  strength  ? 

Our  muscles,  as  well  as  the  food  from  which  they  are 
formed,  consist  of  complex  molecules.  When  they  are  oxidized, 
potential  energy  becomes  kinetic. 

24.  Does  the  plant  produce  energy  ?    ' 

No ;  it  only  absorbs  solar  energy,  and  becomes  the  medium 
of  its  transformation. 

25.  If  we  1>nrn  an  organic  body  in  a  stove  it  gives  off 
heat;  in  the  animal  body  it  produces  also  motion.     Ex- 
plain. 

The  force  set  free  by  the  oxidation  of  the  muscles,  and  of 
the  food  within  the  body,  is  converted  into  muscular  energy. 

2(>.  Why  does  not  blowing  cold  air  on,  a  fire  ivith  a  bel- 
lows  extinguish  it  ? 

It  may  extinguish  it  if  the  blast  be  strong  enough.  If  not 
strong  enough  to  cool  it  below  its  kindling  point,  the  heat  of 
oxidation  more  than  balances  the  cooling  from  the  air. 

27.  IVJiy  docs  bloiving  on  a  fire  hlndle  it,  and  on  a 
lighted  lamp  extinguish  it ? 

The  answer  to  the  previous  question  applies  to  this  one  also. 

28.  Why  can  we  not  ignite  hard  coal  with  a  match  ? 

The  heat  of  the  match  is  not  enough  to  decompose  the  coal, 
and  thus  set  free  gaseous  constituents  for  the  production  of  flame. 

29.  Why  ivill  an  excess  of  coal  put  out  a  fire  ? 

The  coal  is  heated  at  the  expense  of  the  fire,  and  may  reduce 
this  below  the  kindling  point  unless  the  supply  of  O  is  rapid. 

30.  Could  a  light  be  extinguislied  by  merely  lowering 
the  temperature  ? 

Yes ;  by  contact  of  a  large  body  that  is  a  good  conductor 
of  heat. 


66  ANSWERS    TO    PRACTICAL     QUESTIONS 

31.  Why  is  it  beneficial  to  stir  a  wood-fire,  but  not  one 
of  anthracite  coal? 

The  gaseous  constituents  of  wood  are  more  easily  separated 
than  those  of  coal,  but  the  heat  evolved  in  combustion  is  less. 
When  once  well  started,  the  combustion  of  the  coal  is  hence 
more  apt  to  be  self-sustaining. 

32.  Why  ivill  water  put  out  a  fire  ? 

It  absorbs  more  heat  in  proportion  to  its  weight  than  any 
other  known  substance  does  in  changing  from  liquid  to  gas. 
The  production  of  steam  is  hence  at  the  expense  of  the  heat  of 
combustion,  and  the  fuel  is  soon  cooled  below  its  kindling  point. 

33.  What  should  we  do  if  a  person's  clothes  talce  fire  ? 

Smother  the  flame  by  wrapping  the  person  as  quickly  as 
possible  with  a  rug,  coat,  blanket,  or  any  thing  of  this  kind  that 
may  be  at  hand.  If  water  be  near,  throw  it  abundantly  on 
the  burning  garment.  .  . 

34.  Ought  the  doors  of  a  burning  house  to  be  thrown 
open?  » 

No,  except  for  the  purpose  of  getting  out  of  it.  The  in- 
creased supply  of  air  through  the  opening  promotes  the  com- 
bustion. 

35.  Hoiv  much  O  can  be  obtained  from  1OO  grams  of 

Iff/0? 

HgO  :   O  :  :  100  :  x. 

216  :  16  :  :  100  :  x. 
x  =  7.4+,  grams. 

30.  What  would  be  the  volume  of  the  O  of  Question  35 
under  the  standard  conditions  ? 

7.4-*-  1.43  =  5.17  liters. 

37.  JVJiat  would  be  the  volume  of  the  O  at  12°  C.  and 
under  a  pressure  of  74O  mm.  of  mercury  ? 

x  =     *     x  5-17  =  5-42 + ' liters- 


IN    POPULAR     UHEMISTKT.  67 

38.   What  would  be  the  volume  of  the  O  of  Question  16 
tit  2O*  C.  and  75O  nun.  ? 

1.55     293     760 


39.  How  much  KCIOS  must  be  employed  to  maize  an 
amount  of  O  which  shall  measure  1OO  liters  at  18°  C.  and 
7<>O  mm.  ? 

First  find  how  many  liters  of  O  under  standard  conditions 
wo  aid  be  expanded  to  100  liters  at  18°  C.,  the  given  pressure, 
760  mm.,  being  itself  standard.  Call  the  result  V.  It  is 

273_x_100 
~291      * 

Each  of    these   liters  weighs   1.43   grams  ;    hence,  the   total 

weight  is 

27,300x1.43 

291 

Let  x  =  the  required  weight  of  KC1O3. 
Then  03  :  KC1O3  :  :  W  :  x. 

27,300x1.43 
48:    122.5::  --  ^_  -  :  x. 

Hence,  _  27,300x1.43x122.5 

~291x48 

x  =  342.4  grams. 

37—1.  Hoiv  could  you  detect  any  free  O  in  ajar  ofN? 

By  passing  into  it  some  NO  (see  p.  34).  It  will  combine 
with  the  free  O,  forming  red  fumes  of  NOa. 

2.  Hoiv  would  you  remove  the  product  of  the  test  ? 

By  allowing  the  mixture  to  stand  over  water,  which  will 
dissolve  the  NO2. 

3.  In  the  experiment  shown  in  Fig.  ,9,  why  is  the  gas 
red  in  the  flask,  but  colorless  when  it  bubbles  up  into  the 
jar  ? 


68  AXSWRRS    TO    PRACTICAL     QUESTIONS 

In  the  flask,  one  fifth  of  the  atmosphere  was  free  O,  which 
produces  NOa  with  the  NO  as  soon  as  this  is  evolved.  In  the 
jar  there  is  no  free  O. 

4.  How  much  NH3  can  be  obtained  from  3  {/rams  of 
sal-ammoniac  ? 

From  the  reaction,  2NH4Cl  +  CaO  =  2NH3  +  H2O  +  CaCl2,  we 
see  that  for  every  molecule  of  NH4C1  used  we  obtain  one  mole- 
cule of  NH3.  Hence, 

NH4C1  :  NH3  :  :  3  :  x. 
53.5  :  17  :  :  3  :  x. 
x  =  .95  +  ,  gram. 

ft.  What  will  be  the  volume  of  the  NHZ  at  2O°  C.  and 
770  mm.  ? 

Taking  H  as  our  standard,  the  density  of  NH3  is  half  its 
molecular  weight,  or  :  —  ^  —  ,  =  8.5.  The  density  of  O  is  16,  and 
a  liter  of  it  weighs  1.43  grams.  Hence,  a  liter  of  NH3  weighs 
-jr  xl.43  grams,  or  almost  exactly  .76  gram.  The  volume  oc- 
cupied by  .95  gram  of  NH3  under  standard  conditions  is  hence 

'-153  of  a  liter,  or  1.25 
.76 

quired  volume  will  be 


'-153  of  a  liter,  or  1.25  liters.     At  20°  C.    and   770  mm.  the  re- 
.76 


_293     760 

~273X770  ' 

x  =  1.324  liters. 

0.  How  much  H2O  will  be  formed  in  the  process? 

From   the    reaction   we    see   that   one    molecule    of    H2O  is 
formed  for  two  molecules  of  NH4C1.     Hence, 

2NH4C1 :  H3O  : :  3  :  x. 
107  :  18      : :  3  :  x. 


7.  How  much  CaO  ivlll  be  needed  ? 

From  the  reaction  we  see  that  one   molecule  of  CaO  is  re- 
quired with  two  molecules  of  NH4C1.     Hence, 


IX    POPULAR     CHEMISTRY.  69 

2NH4C1  :  CaO  :  :  3  :  a?. 
107  :  56    :  :  3  :  cc. 

x  =  1.57  grams. 

«S.  How  much  N2Ocanbe  made  from  1  gram  of  am- 
monium nitrate  ? 

The  reaction  is 

NH4NO3  =  2H2O  +  N20. 
Hence,  NH4NO3  :  NSO  :  :  1  :  x. 

80  .   44    :  :  1  :  x. 
x  =  .55  gram. 

.9.  How  much  nitric  acid  can  be  formed  from  5O  kilos 
of  sodium  nitrate  (NaNO*)? 

The  reaction  is 


Hence,  NaNO3  :  HNO3  :  :  50  :  x. 

85  :      63      :  :  50  :  x. 
x  =  37  +  ,  kilograms. 

1  O.  What  causes  flesh  to  decompose  so  much  more  easily 
than  wood  ? 

It  is  partly  owing  to  the  greater  complexity  of  its  molecule, 
and  partly  to  the  presence  of  the  N,  which  is  very  unstable  in 
its  compounds. 

11.  If  a  tuft  of  hair  be  heated  wi  a  lest  tube,  the  liquid 
formed  ivill  turn  red  litmus-paper  blue.    Explain. 

Ammonia  is  formed  by  the  decomposition  of  the  hair,  and 
this  acting  on  the  red  litmus-paper,  turns  it  blue. 

12.  Why  should  care  be   used  in  opening  a  bottle  of 
strong  H3N  in  a  warm  room? 

The  space  above  the  liquid  is  filled  with  ammonia  gas, 
which  had  been  dissolved  in  the  water  at  a  low  temperature. 
Its  expansive  force  is  greatly  increased  when  the  temperature 
is  raised.  When  the  stopper  is  removed,  therefore,  a  concussion 
may  result. 


70  ANSWERS    TO    PRACTICAL     QUESTIONS 

13.  What  weight  of  Nis  there  in  1O  grams  of  HNOZ  ? 

HNO3  :  1ST  :  :  10  :  x. 
63  :  14  :  :  10  :  x. 
x  =  2.2  grams. 

14.  Hoiv  much    sal-ammoniac    would  be  required  to 
make  2O  liters  of  NHZ  measured  at  25°  C.  and  744  mm.  ? 

Refer  to  the  answer  of  Question  5.  A  liter  of  NH3  under 
standard  conditions  weighs  .76  gram. 

First  find  how  many  liters  of  NH3  at  0°  C.  and  760  mm. 
are  required  to  expand  to  20  liters  at  25°  C.  and  744  mm. 
Call  the  result  V.  Then 


Each  of  these  weighs  .76  gram.     Call  the  result  W. 
Then  NH3-    NH4C1  :  :  W  :  x. 

17.      '107      ..273x744x20x.76 

298  x  760 
-  107  x  273  x  744  x  20  x.  76 

17x298x760 
x  =  85.8  grams. 

15.  What  is  the  difference  between  liquid  ammonia  and 
liquor  ammonice  ? 

Liquid  ammonia  is  the  result  of  condensing  the  gas  by  cold. 
Liquor  ammoniae  is  the  commercial  name  often  applied  to  the 
solution  of  the  gas  in  water. 

52—  1.  Why,  in  filling  the  hydrogen  gun,  do  ive  use  5 
parts  of  common  air  to  2  of  II,  and  only  one  part  of  O  to  2 
ofH? 

Because  the  air  is  only  £  oxygen,  and  hence  5  parts  of  com- 
mon air  are  equivalent  to  1  part  oxygen. 

2.  Why  are  coal  cinders  often  moistened  with  Hs  O  be- 

fore using  ? 

(See  Popular  Chemistry,  p.  45,  note.) 

The  H2O  being  decomposed  by  the  heat  of  the  fire  increases 
the  combustion. 


IN    POPULAR     CHEMISTRY.  71 

3.  IFJiat  injury  may  be  done  by  throwiny  a  small  quan- 
tity of  H2  O  on  a  fire  ? 

"No  more  heat  is  produced  by  the  action  of  the  H2O,  but 
it  is  in  a  more  available  form  for  communicating  heat.  The 
steam  in  contact  with  incandescent  charcoal  is  decomposed — the 
O  going  to  the  C  to  form  CO2,  and  the  H  being  set  free.  If 
the  C  is  abundant,  and  the  heat  high,  the  CO8  is  also  decom- 
posed, and  double  its  volume  of  CO  formed.  The  inflammable 
gases,  H  and  CO,  mingled  with  the  hydrocarbons  always  pro- 
duced, are  ignited,  making  the  billows  of  flame  which  sweep 
over  a  burning  building." — S.  P.  SHARPLES. 

4.  IVliy  does  the  hardness  of  ^vater  vary  in  different 
localities  ? 

The  hardness  of  the  water  will  necessarily  vary  with  the 
solubility  of  the  minerals  in  different  localities. 

5.  What  causes  the  variety  of  minerals  in  the  ocean  ? 
Is  the  quantity  increasing  ? 

The  ocean  contains  the  washings  of  the  land.  Every  min- 
eral soluble  in  water  is  borne  to  the  sea.  The  quantity  of  min- 
eral matter  in  the  ocean  would  therefore  seem  to  be  increasing, 
yet  there  is  a  compensation  in  the  return  to  the  soil,  of  guano, 
marine  plants,  and  fish,  which  are  driven  on  shore  by  winds 
and  waves,  or  carried  by  the  industry  of  man. 

Analysis  of  sea- water  (Schweitzer) : 

Water 063. 74 

Sodium  chloride 28.05 

Potassium  chloride ...  .76 

Magnesium  chloride 3.66 

Magnesium  bromide .02 

Magnesium  sulphate 2.29 

Calcium  sulphate  1.40 

Calcium  carbonate , .03 

Iodine traces 

Ammonia traces 


1,000.00 

6.  Is  there  not  a  compensation  in  the  sea-plants,  fish, 
etc.,  which  are  washed  back  on  the  land  ? 

(See  Answer  to  Question  5.) 


72  ANSWERS    TO    PRACTICAL     QUESTIONS. 

7.  Since  "  all  the  rivers  flow  to  the  sea/'  ivliy  is  it  not 
full? 

Because  of  the  constant  evaporation  from  its  surface. 

8.  What  is  the  cause  of  the  tonic  influence  of  the  sea- 
breeze? 

There  are  traces  of  certain  minerals  which  probably  give  to 
the  sea-breeze  a  bracing  influence.  The  air  from  the  ocean  is 
also,  doubtless,  highly  ozonized.  It  is  free  from  the  contamina- 
tions that  so  often  make  the  atmosphere  of  the  cities  and  parts 
of  the  country  unhealthy. 

9.  When  fish   are  taJcen   out  of  the  water,  and  thus 
brought  into  a  more  abundant  atmosphere,  ivhy  do  they 
die? 

Fish  inhale  O  through  the  fine,  silky  filaments  of  their  gills. 
When  a  fish  is  drawn  out  of  H2O,  these  dry  up,  and  it  is  un- 
able to  breathe,  although  it  is  in  a  more  plentiful  atmosphere 
than  it  is  accustomed  to  enjoy. 

1  0.  Do  all  fish  die  ivhen  brought  on  land  ? 

No.  Some  fish  have  an  apparatus  for  moistening  their  gills. 
They  can  therefore  crawl  about  in  the  grass,  and  even  migrate 
from  one  stream  to  another. 

1  /.  What  weight  of  water  is  there  in  1OO  Ibs.  of  sodium 
sulphate  (Na2SO4,  1OH2O),  or  Glauber9s  salt? 

10H2O  :  NasSO4,  10H,O  :  :  x  :  100  Ibs. 
180  :  322  :  :  x  :  100  Ibs. 

322  x  =  18,000  Ibs. 

a  =  55.9  Ibs.  (H2O). 


J2.   Wliat  weight  of  water  in   a  ton  of    alum  (KA19 
12H2O}? 

12H3O  :  KA1,  2SO4,  12H2O  :  :  x  :  2,000  Ibs. 
216:  474.5  :  :  x  :  2,000  Ibs. 

474.5  x  =  432,000  Ibs. 

x  =  910.4  Ibs.  (H2O). 

13.  How  does  the  air  purify  running  water? 


IN    POPULAR     CHEMISTRY.  73 

The  O  contained  in  the  air  absorbed  by  the  H2O  oxidizes 
the  organic  substances,  which  are  the  most  dangerous  impuri- 
ties. 

14:.  WJiatis  the  action  of  potassium,  permanganate  as 
a  disinfectant  ? 

It  gives  up  its  O  to  oxidize  the  organic  impurities. 

15.  What  weight  of  II  can  be  obtained  from  a  liter  of 
water  ? 

The  weight  of  a  liter  of  water  under  standard  conditions  is 
1,000  grams.     Of  this   £   is   H.     Hence,  the  required  weight  is 
grams. 


16.  Hoiv  much  Zn  must  be  employed  to  obtain  1OO 
grams  of  H  from  H<>SO±  ? 

The  reaction  is 

Zn  +  H8SO4  =  ZnSO4  +  2H. 
Hence,  2H  :  Zn  :  :  100  :  x. 

2  :  65  :  :  100  :  x. 
x  =  3,250  grams. 

17.  A  liter   of  H  under   standard  conditions  weighs 
O.O896  grant.     What  volume  of  Hat  1O°  C.  and  738  mm. 
can  be  obtained  from  H^SO^  by  the  action  of  8  Jcilos  of 

Zn? 

Zn  +  H2SO4  =  ZnSO4  +  2H. 

Zn  :  2H  :  :  8,000  :  x  in  grams. 
65  :    2    :  :  8,000  :  x. 

x  =  246.15  grams. 

The  number  of  liters  under  standard  conditions  is 
246.15 
.0896  ' 

At  10°  C.  and  738  mm.,  the  volume  is 
_  246.15     283     760 
"  70896"  X  273  X  738' 
V  =  2932.7  liters. 

IS.  How  much  KCIO3  would  be  required  to  evolve  suffi- 
cient O  to  burn  the  H  produced  by  the  decomposition  of  2 
grams  of  HZO? 


74  ANSWERS    TO    PRACTICAL     QUESTIONS 

The  weight  of  H  from   2   grams  of  H2O  is  f  gram.     The 
weight  of  O  required  to  unite  with  it  is  8xf,  or  -1/-  giam. 


3O  : 

48:    122.5  ::%«-:  x. 
x  =  4.537  grams. 

19.  How  much  O  would  be  required  to  oxidize  the  me- 
tallic Cu  which  could  be  reduced  from  its  oxide  by  passing 
over  it9  when  ivhite-hot9  2O  grams  of  H  gas? 

The  amount  required  to  oxidize  the  Cu  is  obviously  the 
same  as  that  which  would  be  separated  from  the  CaO  by  re- 
duction. The  number  of  grams  of  O  thus  separated  must  be  8 
times  the  weight  of  the  H,  or  160  grams. 

20.  How  much  O  would  be  required  to  oxidize  the  me- 
tallic Fe  which  could  be  reduced  in  the  same  manner  by  1O 
grams  of  H  gas  ? 

To  oxidize  10  grams  of  H  would  require  80  grams  of  O.  If 
this  be  withdrawn  from  the  oxide  of  iron,  the  same  amount 
would  be  required  to  oxidize  the  iron  thus  reduced. 

21.  Why  are  rose-balloons  so  buoyant  ? 

Because  the  H  which  they  contain  displaces  air  that  is 
more  than  14  times  as  heavy. 

22.  How  much  H  must  be  burned  to  produce  a  ton  of 
water  ? 

A  ton  is  2,000  pounds.  The  weight  of  H  in  a  ton  of  watei 
is  $  x  2,000,  or  222f  pounds.  To  find  the  volume  of  this  we  re^ 
member  that  the  weight  of  100  cubic  inches  of  air  is  31  grains 
(see  Popular  Physics,  p.  131).  In  every  5  parts  of  air  there  are 
4  parts  of  1ST,  weighing  14  times  as  much  as  the  same  volume 

of  H,  and  1  part  of  O,  weighing  16  times  as  much  ;  —  —  ~  -- 

o 

=  14.4,  nearly.     Hence,  air  is  about  14.4  times  as  heavy  as  H. 
Therefore    31    grains    will   be    the   weight   of    100  x  14.4    cubic 

inches  of  H,  or  of   ^-=~-Q  of  a  cubic  foot  of  H.     To  reduce  the 

i,  i  ,00 


77V    POPULAR     CHEMISTRY. 


7o 


given  weight,  222|  pounds,  to  grains,  we  multiply  by  7,000,  the 

14,000,000 
number  of  grains  in  a  pound,  making  — : — ^ —  grains. 


Then 


14,000,000      1,440 


9 

:  x  in  cubic  feet. 


9          ' '  1,728 
x  —  41,817  cubic  feet. 

This  would  be  enough  to  fill  a  spherical  balloon  43  feet  in 
diameter. 

84 — 1.   IVliy  will  pine-wood   ignite   more   easily  than 
maple  ? 

It  is  richer  in  hydrocarbons,  that  are  readily  volatile. 

2.  Wliy    is  fire-damp    more  dangerous    tlian    cholte- 
damp  ? 

Fire-damp,  CH4,  contains  no  O.  At  the  appropriate  tem- 
perature of  kindling,  when  mixed  with  air,  it  is  a  dangerous 
explosive.  Choke-damp,  CO2,  is  already  a  stable  compound  con- 
taining the  largest  proportion  of  O  that  can  unite  with  C.  It 
is,  therefore,  not  explosive. 

3.  Hepresent  the  reaction  in  malting  CO2,  shoiving  the 
atomic  weights,  as  in  the  preparation  of  O  on  page  12. 


(40+12  +  48)  +  2  (1  +  35. 5)  =  (40 +  71) +  (2 +  16) +  (12 +  32). 
100  +  73  =  111  +  18  +  44. 
173  =  173. 

4.  Should  one  taJce  a  light  into  a  room  where  the  gas  is 
escaping  ? 

No.  An  important  constituent  of  illuminating  gas  is  the 
dreaded  fire-damp,  CH4.  Mixed  with  the  air  in  the  room,  it 
may  be  exploded  by  introducing  a  lighted  match  or  candle. 

5.  irtiy  does  it  dull  a  Jcnife  to  sharpen  a  pencil  ? 

The  particles  of  graphite  in  the  pencil  are  very  hard,  and 
the  knife  edge  is  worn  away  by  friction. 

6.  Where  was  the  C,  now  contained  in  the  coal,  before 
the  Carboniferous  age  ? 

Probably  most  of  it  was  combined  with  O,  forming  CO3  in 
a  densely  charged  atmosphere. 


76  ANSWERS    TO    PRACTICAL     QUESTIONS 

7.  Must  the  air  have  then  contained  more  2>lctnt  food  ? 

Probably  it  did. 

8.  What  is  the  principle  of  the  aquarium  ? 

The  inter-dependence  of  animals  and  plants,  whereby  each 
supplies  the  wants  of  the  other.  The  aquarium  is  a  microcosm 
— a  world  in  miniature.* 

*  I  have  read  somewhere  a  beautiful  Persian  fablo  in  which  a  nightin- 
gale and  a  rose  are  represented  as  being  confined  in  a  cage  together,  and 
being  dependent  upon  each  other  for  life.  The  fable  is  truth  symbolized. 
The  idea  has  now  become  more  practical,  but  not  less  beautiful.  In  the 
modern  aquarium,  or  drawing-room  fish-pond,  we  see  the  world  in  minia- 
ture. It  is  a  self-regulating,  self-subsisting  establishment,  and  is  con- 
structed on  the  most  perfect  principles  of  chemical  economy. 

"  Before  this  truth  of  compensation  between  animals  and  plants  was 
discovered,  many  attempts  were  made  to  keep  fish  in  small  glass  globes. 
As  they  soon  exhausted  the  oxygen,  and  impregnated  the  water  with  car- 
bonic acid,  it  was  necessary  to  change  it  daily.  Finally,  but  a  few  years 
since,  it  was  discovered  that  plants  evolve  oxygen  and  consume  carbonic 
acid  in  the  water  as  well  as  in  the  air.  Starting  out  with  this  idea,  about 
the  year  1850,  a  Mr.  "Warrington,  an  Englishman,  set  about  breeding  fish 
and  mollusks  in  tanks  by  the  aid  of  marine  plants.  He  succeeded  admi- 
rably for  a  few  days,  but  after  a  time  a  change  came  over  his  little  world. 
Without  apparent  reason,  the  water  became  suddenly  impure,  and  the  fish 
died.  Here  was  a  new  agency  at  work.  "With  the  aid. of  a  microscope,  Mr. 
Warrington  explored  his  tank  for  the  poison  that  was  evidently  latent 
there.  He  soon  discovered  that  some  of  his  plants  had  reached  maturity, 
and,  in  obedience  to  the  law  of  nature,  had  died.  The  decaying  matter 
was  the  poison  of  which  he  was  in  search.  How  was  this  to  be  counter- 
acted? In  nature's  tanks— seas,  rivers,  and  ponds— reflected  Mr.  Warring- 
ton,  plants  must  die  and  decay,  yet  this  does  not  destroy  animal  life.  Wo 
must  see  how  nature  remedies  the  evil.  He  hastened  to  a  pond  in  the 
vicinity,  and  examined  its  bottom  with  care.  He  found,  as  he  had  antici- 
pated, an  abundance  of  vegetable  matter  decayed.  He  likewise  found 
swarms  of  water-snails  doing  duty  as  scavengers,  and  devouring  the  putre- 
fying substances  before  they  had  time  to  taint  the  water.  Here  was  the 
secret ;  so  beautiful  a  contrivance  that  it  is  said  Mr.  Warrington  burst  into 
tears  when  it  flashed  upon  him  like  a  revelation. 

"  He,  however,  quickly  dried  his  eyes,  gathered  a  quantity  of  snails, 
and  threw  a  handful  into  his  little  tank  at  home.  In  a  single  day  the 
water  was  clear  and  pure  again.  The  fish  throve  and  gamboled,  grew  and 
multiplied ;  the  plants  resumed  their  bright  colors,  and  the  snails  not  only 
rollicked  in  an  abundance  of  decaying  branches,  but  laid  a  profusion  of 
eggs,  on  which  the  fish  dined  sumptuously  every  day." 


IN    POPULAR     CHEMISTRY.  77 

.9.  What  test  should  be  employed  before  going  down  in 
an  old  ivell  or  cellar  ? 

A  lighted  candle  should  be  lowered.  If  that  is  dimmed  or 
extinguished,  it  is  not  safe  for  one  to  descend. 

10.  What  causes  the  sparkle  of  wine  and  the  foam  of 
beer? 

The  CO3  formed  in  the  process  of  fermentation. 

11.  What  causes  the  cork  to  fly  out  of  a  catsup  bottle  ? 

The  CO 3  which  is  produced  when  the  catsup  ferments. 

12.  What  physical  principle  does  the  solidification  of 
CO2  illustrate  ? 

That  evaporation  is  a  cooling  process.  A  portion  of  the 
liquid  CO3  turns  to  vapor,  and  thus  abstracts  so  much  heat 
from  the  remainder  as  to  freeze  it.  (See  Popular  Physics,  p. 
255.) 

13.  Why  does  the  division  in  the  chimney  shown  in 
Fig.  29  produce  tivo  currents  ? 

For  a  few  moments  there  is  an  uncertainty — a  condition  of 
unstable  equilibrium.  The  heated  air  is  tending  to  rise,  and 
the  cold  air  tending  to  come  in  to  supply  its  place.  The  situ- 
ation of  the  candle  in  the  jar  determines  the  length  of  time 
before  the  currents  start.  If  the  candle  be  placed  on  one  side 
of  the  jar,  they  will  be  established  almost  instantly. 

14.  What  causes  the  unpleasant  odor  of  coal-gas?    Is 
it  useful  ? 

Impurities  which  it  contains.  Olefiant  gas  has  a  faint 
sweetish  odor,  while  carbonic  oxide  and  hydrogen,  when  pure, 
are  inodorous.  The  disagreeable  smell  is  due  in  part  to  acety- 
lene (C2H2).  The  unpleasant  odor  warns  us  of  the  presence  of 
coal-gas. 

15.  irJiat  causes   the  sparkling  often  seen  in  a  gas- 
light? 

Particles  of  solid  taken  up  mechanically  in  the  process  of 
purification,  or  otherwise. 


78  ANSWERS    TO    PRACTICAL     QUESTIONS 

16.  Why    does   H  in    burning    give    out    more    heat 
than  C? 

1  Ib.  of  H  burned  in  O  emits  heat  sufficient  to  melt  315.2 
Ibs.  of  ice ;  and  12  Ibs.  of  carbon  converted  into  CO2  enough  to 
melt  700  Ibs.  of  ice.  (This  subject  is  quite  fully  treated  in 
Miller's  Chemical  Physics,  page  294,  et  seq.)  The  cause  is  not 
as  yet  fully  determined,  although  it  is  perhaps  safe  to  say  that 
in  ordinary  combustion  the  heat  depends  on  the  amount  of  O 
which  enters  into  combination  with  the  fuel. 

1 7.  Wiiy  do  not  stones  burn  as  well  as  ivood  ? 

Because  they  are  already  burned,  i.e.,  combined  with  O. 

18.  Why  does  not  hemlock  make  good  coals? 

Because  (1)  of  its  lack  of  C,  and  (2)  its  porous  structure. 

19.  What  adaptation  of  chemical  affinities  is  shown  in 
a  light  ? 

If  O  had  the  same  affinity  for  C  that  it  has  for  H,  they 
would  be  consumed  at  once,  with  little  light.  The  fact  that 
the  H  burns  first,  and  thus  heats  up  to  the  luminous  point  the 
particles  of  C  as  they  float  outward  to  the  air,  causes  the  illu- 
minating power  of  the  hydro-carbons. 

20.  Why  does  snuffing  a  candle  brighten  the  flame  ? 

Because  it  removes  the  charred  wick,  which  diminishes  the 
heat  of  the  flame  by  both  conduction  and  radiation. 

21.  Wliy  is  the  flame  of  a  candle  red  or  yellow,  and 
that  of  a  kerosene  oil-lamp  white  ? 

(See  Popular  Physics,  p.  243). 

The  heat  of  a  candle-flame  is  much  less  than  that  of  kero- 
sene, and  thus  the  colors  characteristic  of  a  lower  temperature 
are  produced. 

22.  Why  does  a  street  gas-light  burn  blue  on  a  ivindy 
night  ?    Is  the  light  then  as  intense  ?     The  heat  ? 

O  is  mingled  with  the  flame  in  sufficient  quantities  to  burn 
the  H  and  C  simultaneously.  Thereby  the  heat  is  increased, 


IN    POPULAR     CHEMISTRY.  79 

but   the   light   diminished.      The    principle  is  that  of  Bunsen's 
burner. 

23.  Why  does  not  the  lime  burn  in  a  calcium-light  ? 

Lime  is  a  burned  body  ;  its  symbol  is  CaO. 

24.  Why  is  a  candle-flame  tapering  ? 

(See  Chemistry,  p.  77.) 

The  currents  of  air  rushing  toward  the  flame  from  all  sides 
give  it  the  conical  form. 

25.  Why  does  a  draught  of  air  cause  a  light  to  smoke  ? 

It  lowers  the  heat  of  the  flame  below  the  point  of  union 
between  C  and  O,  and  thus  the  C  is  precipitated. 

26.  Wliat  makes  the  coal  at  the  end  of  a  candle-wick  ? 

The  wick  at  the  edge  of  the  flame  comes  in  contact  with 
the  O  of  the  air,  and  therefore  burns. 

27.  Which  is  the  hottest  part  of  a  flame  ? 

Toward  the  point  of  the  cone,  where  the  gaseous  envelopes 
meet  and  make  a  solid  flame. 

28.  Why  does  not  a  candle-wick  burn  eoccept  at  the 
edge  of  the  flame  ? 

There  is  110  O  at  the  center  of  the  flame. 

29.  How  does  a  chimney  enable  us  to  burn  without 
smoke  highly  carboniferous  substances  like  oil  ? 

It  prevents  the  heated  products  of  combustion  from  becom- 
ing mixed  with  cold  air.  These  rise,  and  new  air  can  come  in 
only  at  the  bottom.  The  stronger  the  heat  in  the  chimney  the 
greater  is  this  draught.  A  flame,  in  which  the  combustion  is 
imperfect  when  O  is  supplied  slowly,  becomes  much  brighter 
when  O  is  supplied  fast  enough  to  produce  perfect  combustion 
of  the  H,  and  also  to  oxidize  all  the  C  without  allowing  any  to 
pass  off  as  smoke. 

30.  How  much  COa  in  20O  Ibs.  of  chalk  ? 


80  ANSWERS    TO    PRACTICAL     QUESTIONS 

CO3  :  CaCO3  : :  x  :  200  Ibs. 
44  :      100     :  :  x  :  200  Ibs. 
100  x  =  8,800  Ibs. 
x  =  88  Ibs.  (COS). 

«?./.   What  iveight  of  CO2  in  a  ton  of  marble  ? 

CO2  :  CaCO3  : :  x  :  2,000  Ibs. 
44  :     100     : :  x  :  2,000  Ibs. 
100  x  =  88,000  Ibs. 

x  =  880  Ibs.  (CO3). 

32.  Why  does  not  a  cold  saucer  held  over  an  alcohol 
flame  blacken,  as  it  does  over  a  candle  or  gas-light  ? 

There  is  less  C  in  alcohol  than  in  tallow  or  in  coal-gas. 

33.  How  much  CO2  is  formed  in  the  combustion  of  one 
ton  of  C? 

C  :  CO2  : :  2,000  Ibs.  :  x. 

12  :  44    : :  2,000  Ibs.  :  x. 
12  x  =  88,000  Ibs. 

x  =  7333.33  +  lbs.  (CO3). 

34.  IWiat  weight  of  Cis  there  in  a  ton  of  CO2  ? 

C  :  CO2  :  :  x  :  2,000  Ibs. 

12  :  44   :  :  x  :  2,000  Ibs. 

44  x  =  24,000  Ibs. 

x  =  545.45  +  Ibs.  (C). 

35.  Sow  much  O  is  consumed  in  burning  a  ton  of  C? 

In  any  quantity  of  CO2,  T\  of  the  compound  is  O,  and  JST 
C.  If  T3T  =  2,000  Ibs.  (COo),  then  T8T  =  |  of  2,000  Ibs.  =  5333.33 
+  lbs.  (O). 

36.  IVliat  weight    of  sodium   carbonate  (Na2CO3,  1O 
HSO,  "  carbonate  of  soda")  would  be  required  to  evolve  12 
grams  of  CO2  ? 

CO2  :  Na2CO3  10ELO  : :  12  gm.  :  x. 
44  :  286  : :  12  gm.  :  x. 

44  x  =  2,432  gm. 

x  =  50.72  gm.  (Na2C03,  10HSO). 


IN    POPULAR     CHEMISTRY.  81 


37.  How  much  CO2  will  be  formed  in  the  combustion 
of  3O  gm.  of  CO  ? 

CO  :  CO3  :  :  30  gm.  :  x. 

f  28  :   44    :  :  30  gm.  :  x. 

28  x  =  1,320  gm. 

x  =  47.14  gm.  (CO2). 

38.  What  tveight  of  CaCOs  would  be  required  to  evolve 
12  grams  of  CO2  ? 


CO2  :  CaCO3  :  :  12  :  x. 
44  :  100  :  :  12  :  x. 
x  =  2?!3T  grams. 

39.  What  would  be  the  volume  of  these  12  grams  of 
CO  2  at  12°  C.  and  744  mm.  ? 

The  molecular  weight  of  CO2  [12  +  2(16)],  is  44.  Its  density 
is  therefore  22.  Under  standard  conditions  1  liter  of  H  weighs 
.0896  gm.  ;  therefore  1  liter  of  CO2  weighs  22  x.  0896  gm.,  or 
1.97  gm.  The  number  of  liters  that  would  weigh  12  gm.  is 

12 

hence  :r7r^,  or  6.09  liters.      At  12°  C.  and  744  mm.  this  volume 
1.97 

would  be  expanded  to 

Ar  285  760  _no 
V==273X^4x6m 
V  =  6.494  liters. 

40.  Hoiv  much  C  would  be  necessary  to  furnish  CO2 
enough  to  fill  a  gas-holder  1O  meters  high  and  4  meters  in 
diameter  when  the  temperature  is  25°  C.,  and  the  barome- 
ter stands  754  mm.  ? 

First  find  the  capacity  of  the  gas-holder.  The  volume  of  a 
cylinder  is  equal  to  its  length  multiplied  by  the  area  of  its 
cross  action.  In  this  case  it  is  10  x  3.1416  x(2)a,  or  125.664 
cubic  meters.  Since  in  a  cubic  meter  there  are  1,000  liters,  this 
volume  is  125,664  liters,  the  temperature  being  25°  C.,  and  the 
pressure  754  mm.  Reducing  this  to  standard  conditions,  we 

070      7^4. 
have  V  =  125,664  x  ™  x™ 

V  =  114,810.5  liters. 


82 


ANSWERS    TO    PRACTICAL     QUESTIONS 


Each   of  these   liters   of  CO2  weighs   1.97   gm.   (see   answer 
to  Question  39).     Hence  the  total  weight  of  CO2  is  114,210.5  x 

1.97  =  224,995  gm. 

CO3:C    ::  224,995  :  x. 

44  :  12  :  :  224,995  :  x. 
x  =  61.362T3T  grams. 
Or  x  =  61.362  + ,  kilograms. 

41.   Write  in  double  columns  the  different  properties  of 
carbon  dioxide  and  carbon  monoxide  ;  thus, 


CO2  is  1,  non-inflammable. 

2.  Atomic  weight— 44. 

3.  Specific  gravity— 1.529. 

4.  Will  not  burn. 

5.  A  negative  poison. 

6.  Liquefies  at  32°,  and  a  press- 

ure of  38.5  atmospheres. 

7.  Freely  soluble  in  H2O. 

8.  Forms  salts. 

Etc.,  etc. 


CO  is  1,  inflammable. 

2.  Atomic  weight— 28. 

3.  Specific  gravity— .967. 

4.  Burns  with  a  blue  flame. 

5.  A  direct  poison. 

6.  Has  never  been  liquefied. 

7.  Sparingly  soluble  in  water. 

Etc.,  etc. 


I  IO — 1.  If  chlorine  iv at er  stands  in  the  sunlight  for  a 
time,  it  ivill  only  redden  a  litmus-solution.  Why  does  it 
not  bleach  it  ? 

Hydrochloric  acid  is  formed,  which  reddens  the  litmus. 

2.  Why  do  tinsmiths  moisten  with  HCl,  or  sal-ammo- 
niac, the  surface  of  metals  to  be  soldered  ? 

It  dissolves  the  coating  of  oxide,  and  leaves  the  surface  of 
the  metal  free  for  the  action  of  the  solder. 

3.  How  much  HCl  can  be  made  from  25  kilos  of  com- 
mon salt  ? 

NaCl :    Cl    : :  25  :  x. 

58.5  :  35.5  :  :  25  :  x. 

x  —  15.17  kilograms. 

4.  What  weight  of  NaCl  would  be  required  to  form  25 
kilos  of  HCl? 


IN   POPULAR     CHEMISTRY.  83 


Each  molecule  of  NaCl  thus  yields  one  molecule  of  HC1. 
HC1  :  NaCl  :  :  25  :  x. 
36.5  :   58.5  :  :  25  :  x. 
x  =  40  +  ,  kilograms. 

5.  HCl  of  a  specific  gravity  of  1.2  contains  about  4O 
per  cent,  of  the  gas.  This  is  very  strong  commercial  acid. 
What  weight  could  be  formed  by  the  HCl  gas  produced  in 
the  reaction  named  in  the  preceding  problem  ? 

25  kilos  =  .40  x. 
x  =  ~=  62.5  kilos. 

•  4vJ 

f>.  What  is  the  difference  betiveen  sublimation  and  dis- 
tillation ? 

A  body  is  said  to  sublime  when  it  rises  as  vapor  and  con- 
denses in  the  solid  form  ;  when  it  condenses  as  a  liquid  it  is 
said  to  distil. 

7.  Why  do  eggs  discolor  silver  spoons  ? 

The  sulphur  of  the  egg  combines  with  the  Ag,  forming 
silver  sulphide. 

8.  Explain  the  principle  of  hair-dyes. 

The  two  principal  chemicals  used  for  dyeing  the  hair  are 
lead  and  silver  nitrate.  The  S  in  the  hair  combining  with  the 
Ag  makes  silver  sulphide,  or  with  the  Pb,  lead  sulphide,  either 
of  which  stains  the  hair  ;  the  former  colors  the  skin  as  well  as 
the  hair,  while  the  latter  is  absorbed  through  the  skin,  causing 
colics  and  other  diseases  such  as  are  common  among  painters. 
The  "golden  yellow  color"  lately  in  fashion  is  produced  by  a 
solution  of  arsenic  with  the  hydrosulphate  of  ammonia.  In  or- 
der to  dye  the  lighter  tints,  it  is  necessary  to  bleach  the  hair 
with  an  alkaline  solution.  See  Fireside  Science,  page  77. 

9.  Ts  it  safe  to  mix  oil  of  vitriol  and  water  in  a  glass 
bottle  ? 

The  heat  produced  by  the  combination  of  the  two  will  be 
liable  to  break  the  glass. 


84  ANSWERS    TO    PRACTICAL     QUESTIONS 

10.  What  is  the  color    of  a  sulphuric  acid  stain    on 
cloth  ?    How  ^vould  you  remove  it  ? 

It  is  generally  red,  especially  on  black  woolen  cloth.  The 
color  may  be  restored  by  a  few  drops  of  a  solution  of  common 
"soda,"  or  ammonia. 

11.  What  causes  the  milky  look  when  oil  of  vitriol  and 
water  are  mimed  ? 

Pb  from  the  stills  in  which  the  acid  is  condensed,  and  which 
is  soluble  in  strong  H3SO4,  is  precipitated  when  the  acid  is  di- 
luted with  H2O. 

12.  What  is  the  chemical  relation  bettveen  animals  and 
plants  ?     Wliich  perform  the  office  of  reduction,  and  which 
of  oxidation  ? 

The  animal  lives  on  organized  materials,  taking  up  O  and 
evolving  COS,  and  other  oxidized  products.  The  plant  lives  on 
unorganised  materials,  CO2,  HO,  NH3,  and  salts,  organizing 
them  and  evolving  O.  The  function  of  the  animal  is  oxidation ; 
that  of  the  plant,  reduction.  The  food  of  the  plant  serves 
merely  to  increase  its  bulk  ;  that  of  the  animal  is  employed  to 
replace  the  material  worn  out  by  the  active  operations  of  life. 
The  animal  obtains  the  energy  necessary  for  its  existence  from 
the  oxidation  of  its  own  body  ;  the  plant  obtains  the  energy 
necessary  for  the  organization  of  its  food  directly  from  the 
sun. 

13.  How  many  pounds  of  S  are  contained  in  1OO  Ibs. 

of  H2SOt  ? 

S  :  H2SO4  : :  x  :  100  Ibs. 

32  :      98      : :  x  :  100  Ibs. 
98  x  =  3,200  Ibs. 
x  =  32ff  Ibs.  (S). 

14.  How  much  O  and  H2  O  are  needed  to  change  a  ton 
of  8O2  to  JT2S04  ? 

One  ton  of  SOa  will  make  1££  tons  of  HaSO4  :  of  which  ?V 
is  H,  if  is  S,  and  f-f  is  O.  £  of  this  O,  or  ¥8T,  comes  from  the 


IN   POPULAR     CHEMISTRY.  85 

air,  and  %  =  -4\  from  the  water.  (See  process  of  manufacture, 
Chemistry,  p.  106.)  Hence,  ^  (O)  and  ^  (R)=&  of  the  acid, 
was  furnished  by  the  water—  &  of  l£f.  tons  =  ^  ton  (H2O). 


1  J.  Hoiv  much  O  in  a  Ib. 

f  f  of  any  quantity  of  sulphuric  acid  are  O  ;  ?V  is  H  ;  and 
If  are  S.     Hence,  in  1  Ib.  of  H2SO3  there  are  ff  Ib.  (O). 

16.  State    the  analogy  between    the    compounds  of   O 
and  S. 


O. 

H2O. 

H2O3  (hydrogen  dioxide). 

CO.. 


S. 


H8S2. 
CS2. 


The  corresponding    compounds   possess    not   only  an   analo- 
gous composition,  but  also  similar  chemical  properties. 


1  48  —  !•  fn  the  experiment  with  NazSO±,  on  page 
an  accurate  thermometer  will  show  that  in  making  the  so- 
lution, the  temperature  of  the  liquid  will  fall,  and  in  its 
solidification,  will  rise.  Explain. 

(See  Popular  Physics,  p.  250.) 

Energy  of  temperature  is  absorbed  in  doing  the  work  of 
overcoming  molecular  cohesion  ;  hence,  the  thermometer  falls 
while  the  salt  is  becoming  liquid.  In  returning  to  the  solid 
state  it  gives  out  this  energy  again  as  temperature. 

2.  If,  in  making  a  solution  of  NasSO^,  ive  use  the  salt 
which  lias  effloresced,  and  so  become  anhydrous,  the  tem- 
perature will  rise  instead  of  falling  as  before.    Explain. 

This  is  because  a  solid  hydrate  is  formed  before  the  salt  dis- 
solves in  the  H2O.  The  same  holds  true  of  other  anhydrous 
bodies,  as  the  chlorides  of  Zn,  Fe,  and  Cu. 

3.  IVliy  is  KNOg,  used  instead  of  NaNO^  for  making 
giuipowder  ? 

Sodium  nitrate  is  imported  from  Chili  in  large  quantities, 
and  attempts  have  been  made  to  use  it  for  making  gunpowder,* 

*  Gunpowder  is  an  intimate  mechanical  mixture  of  about  1  part  niter, 
1  part  sulphur,  and  3  parts  charcoal.  These  proportions,  however,  vary 


86  ANSWERS    TO    PRACTICAL     QUESTIONS 

but  its  tendency  to  attract  moisture  has  frustrated  the  plan.  It 
is  now  extensively  used  as  a  fertilizer,  and  is  said  to  be  the 
cheapest  form  in  which  N  can  be  furnished  the  soil. 

4.  Why  is  a  potassium  salt  preferable  to  a  sodium  one 
in  glass-making  ? 

Sodium  salts  give  a  greenish  tint  to  the  glass. 

5.  What  is  the  glassy  slag  so  plentiful  about  a  fur- 
nace ?  * 

A  silicate  of  lime  or  some  other  base  contained  in  the  ore. 

Ordinary  Slag  from  Blast  Furnace  (Bloxam). 

Silica 43.07 

Alumina 14.85 

Lime 28.92 

Magnesia 5.87 

Oxide  of  iron 2.53 

Oxide  of  manganese 1.37 

Potash. 1.84 

Sulphide  of  calcium 1.90 

Phosphoric  acid trace 

100.35 

somewhat  in  different  countries,  as  well  as  in  different  sorts  of  powder. 
More  charcoal  adds  to  its  power,  but  also  causes  it  to  attract  moisture  from 
the  air,  which  of  course  injures  its  quality.  For  blasting  rocks,  where  a 
sustained  force,  rather  than  an  instantaneous  one,  is  required,  the  powder 
contains  more  sulphur,  and  is  even  then  often  mixed  with  sawdust  to  re- 
tard the  explosion.  The  niter,  sulphur,  and  charcoal,  having  been  ground 
and  sifted  separately,  are  thoroughly  mixed,  and  then  made  into  a  thick 
paste  with  water.  This  is  ground  for  some  hours  under  edge-stones,  after 
which  it  is  subjected  to  immense  pressure  between  gun-metal  plates,  form- 
ing what  is  known  as  press-cake.  These  cakes  are  then  submitted  to  the 
action  of  toothed  rollers,  whereby  the  granulation  of  the  powder  is  effected. 
The  grains  thus  formed  are  sorted  into  different  sizes  by  means  of  a  series 
of  sieves,  and  thoroughly  dried  at  a  steam  heat.  The  last  operation,  that 
of  polishing,  is  accomplished  in  revolving  barrels,  after  which  the  powder 
is  ready  for  market.  The  heavier  the  powder,  the  greater  is  its  explosive 
power.  Good  powder  should  resist  pressure  between  the  fingers,  giving  no 
dust  when  rubbed,  and  have  a  slightly  glossy  aspect.— YOTJMANS. 

*  The  slag  is  commonly  employed  for  road-making  in  the  neighborhood 
of  the  iron-works.  Some  attempts  have  been  made  to  turn  the  slag  to  ac- 
count by  employing  it  as  a  manure  for  soils  deficient  in  potash,  of  which 


IN    POPULAR     CHEMISTRY.  87 

6.  State  the  formula?  of  niter,  saleratus,  carbonate  and 
bicarbonate  of  soda,  plaster,  pearlash,  saltpeter,  plaster  of 
Paris,  gypsum,  carbonate  and  bicarbonate  of  potash,  sal- 
soda,  and  soda. 


Niter,  saltpeter 

Saleratus,  pearlash  ........................................  HKCO3. 

Carbonate  of  soda,  sal-soda  ..............................  Na2CO3. 

Bicarbonate  of  soda,  "  soda  "  ............................  H3STaCO3. 

Plaster,  gypsum  ...........................................  CaSO«,2H2O. 

Plaster  of  Paris  ...........................................  CaSO4. 

7.  Explain  hoiv  ammonium  carbonate  is  formed  in  the 
process  of  maMng  coal-gas. 

Nitrogen  exists  in  small  quantities  in  coal,  and  when  that 
is  distilled  at  a  high  temperature,  the  elements  in  their  nascent 
state  combine  to  form  this  compound. 

8.   Upon  what  fact  depends  the  formation  of  stalactites  ? 

Water  containing  carbonic  acid  in  solution  will  dissolve  car- 
bonate of  lime  freely,  but  when,  on  exposure  to  the  air,  the 
gas  escapes,  the  carbonate  is  deposited. 


9.  iniy  is  HF  kept  in  gutta-percha  bottles  ? 

Because  it  will  dissolve  silica,  and  so  destroy  a  glass  bottle. 

10.  Explain  the  use  of  borax  in  washing. 

It  softens  "hard"  water  by  uniting  with  the  soluble  salts 
of  lime  or  magnesia,  and  making  insoluble  ones  which  settle 
and  form  a  thin  sediment  in  the  bottom  of  pitchers  in  which  it 
is  placed. 

11.  How  are  petrifactions  formed  ? 

Certain  springs  contain  large  quantities  of  some  alkaline 
carbonate  ;  their  waters,  therefore,  dissolve  silica  abundantly. 
If  we  place  a  bit  of  wood  in  them,  as  fast  as  it  decays,  parti- 

it  will  be  seen  that  the  above  slag  contains  nearly  g^th  of  its  weight,  in  a 
form  which  would  be  easily  rendered  available  for  plants  by  the  combined 
action  of  air  and  moisture.  When  the  slag  is  run  into  water,  or  blown 
into  a  frothy  condition  by  the  blast,  it  resembles  pumice-stone,  and  is  easily 
ground  to  a  powder  fit  for  applying  to  the  soil. 


88  ANSWERS    TO    PRACTICAL     QUESTIONS 

cles  of  silica  will  take  its  place— atom  by  atom— and  thus  pet- 
rify the  wood.  The  wood  has  not  been  changed  to  stone,  but 
has  been  replaced  by  stone. 

12.  In  what  part  of  the  body,  and  in  ivhat  forms,  is 
pJiosphorus  found  ? 

As  a  phosphate  it  is  tho  principal  earthy  constituent  of  the 
bones.  It  is  also  a  never-failing  ingredient  of  the  brain  and 
nervous  system.  The  susceptibility  of  phosphorus  to  oxidation 
especially  adapts  it  to  the  rapid  changes  incident  to  the  struct- 
ure and  offices  of  the  brain.* 

*  Phosphorus  is  an  element  which  can  imperceptibly  and  quickly  pass 
from  a  condition  of  great  chemical  activity  to  one  of  equal  chemical  inert- 
ness. In  virtue  of  this  character,  it  "  may  follow  the  blood  in  its  changes, 
may  oxidize  in  the  one  great  set  of  capillaries,  and  be  indifferent  to  oxygen 
in  the  other;  may  occur  in  the  brain,  in  the  vitreous  form,  changing  as 
quickly  as  the  intellect  or  imagination  demands,  and  literally  naming  that 
thoughts  may  breathe  and  words  may  burn ;  and  may  be  present  in  the 
bones  in  its  amorphous  form,  content  like  an  impassive  caryatid,  to  sustain 
upon  its  unwearied  shoulders  the  mere  dead  weight  of  stones  of  flesh.  And 
what  is  here  said  of  the  brain  as  contrasted  with  the  bones,  will  apply  with 
equal  or  similar  force  to  many  other  organs  of  the  body.  All  throughout 
the  living  system,  we  may  believe  that  phosphorus  is  found  at  the  centers 
of  vital  action  in  the  active  condition,  and  at  its  outlying  points  in  the 
passive  condition.  In  the  one  case  it  13  like  the  soldier  with  his  loaded 
musket  pressed  to  his  shoulder  and  his  fmger  on  the  trigger,  almost  antici- 
pating the  command  to  fire ;  in  the  other  it  is  like  the  same  soldier  with 
his  unloaded  weapon  at  his  side  standing  at  ease." 

"  Further,  phosphorus  forms  with  oxygen  a  powerful  acid,  capable  even 
of  abstracting  water  from  sulphuric  acid,  and  yet  perfectly  unirritating 
to  the  organic  textures.  Taking  up  varying  quantities  of  water,  phosphoric 
acid  assumes  no  fewer  than  three  distinct  forms,  which  will  unite  with 
one,  two,  or  three  atoms  of  alkali  respectively,  giving  an  acid,  neutral,  or 
alkaline  reaction.  Thus  it  is  available  for  the  most  varied  uses  in  the 
body.  A  child  is  beginning  to  walk,  and  tho  bones  of  its  limbs  must  be 
strengthened  and  hardened ;  phosphoric  acid,  accordingly,  carries  with  it 
three  units  of  lime  to  them,  and  renders  them  solid  and  iirir.  But  the 
bones  of  its  skull  must  remain  comparatively  soft  and  yielding,  for  it  has 
many  a  fall,  and  the  more  elastic  these  bones  are,  the  less  will  it  suffer 
when  its  head  strikes  a  hard  object ;  so  that  in  them  we  may  suppose  the 
phosphoric  acid  to  retain  biit  two  units  of  lime,  and  to  form  a  softer,  less 
consistent  solid.  And  the  cartilages  of  the  ribs  must  be  still  more  supple 
and  elastic,  so  that  in  them  the  phosphoric  acid  may  be  sxipposed  to  be 


IN    POPULAR     CHEMISTRY.  Si) 

13.  Why  are  matches  poisonous?     What  is  the  anti- 
dote ? 

Because  of  the  phosphorus  in  the  match.  Turpentine  has 
been  proposed  as  a  remedy,  but  is  not  known  to  be  reliable. 

14.  Will  the  burning  phosphorus  ignite  the  wood  of  the 
match  ? 

It  does  not  give  off  enough  heat  in  its  oxidation  to  raise  the 
temperature  of  the  wood  to  the  igniting  point.  Some  substance 
of  low  kindling  point,  such  as  sulphur,  or  which  contains  a 
large  amount  of  O,  such  as  KC1O;J,  is  added  to  produce  violent 
oxidation  and  kindle  the  wood. 

15.  What  principle  is   illustrated  in  the  ignition  of  a 
match  by  friction  ? 

The  conversion  of  motion  into  heat. 

l(t.  How  much  HZO  would  be  required  to  dissolve  a 
pound  of  KNOZ  ? 

3i  Ibs.  of  cold  water,  or  i  Ib.  of  hot  water. 

17.  What  causes  the  bad  odor  after  the  discharge  of  a 
gun  ? 

The   potassium   sulphide   gradually  gives   up   its  S  to   form 


combined  with,  but  one  unit  of  base.  On  the  other  hand,  its  teeth  must 
be  harder  than  its  hardest  bones,  and  a  new  demaiid  is  made  on  the  lirae- 
phosphates  to  associate  themselves  with  other  lime-salts  (especially  fluoride 
of  calcium),  to  form  the  cutting  edges  and  grinding  faces  of  the  incisors 
and  molars.  All  the  while,  also,  the  blood  must  be  kept  alkaline,  that  oxi- 
dation of  the  tissues  may  be  promoted,  and  albumen  retained  in  solution  ; 
and  yet  it  must  not  be  too  alkaline,  or  tissues  and  albumen  will  both  be 
destroyed,  and  the  carbonic  acid  developed  at  the  systemic  capillaries 
•will  not  be  exchanged  for  oxygen  when  the  blood  is  exposed  to  that  gas 
at  the  lungs.  So  phosphoric  acid  provides  a  salt  containing  two  units 
of  soda  and  one  of  water,  which  is  sufficiently  alkaline  to  promote  oxida- 
tion, dissolve  albumen,  and  absorb  carbonic  acid,  and  yet  holds  the  latter 
so  loosely,  that  it  instantly  exchanges  it  for  oxygen  when  it  encounters 
that  gas  in  the  piilmonary  capillaries.  Again,  the  flesh  juice  must  be  kept 
acid  (perhaps  in  opposition  to  the  alkaline  blood,  as  affecting  the  trans- 
mission of  the  electric  currents  which  traverse  the  tissues),  and  phosphoric 
acid  provides  a  salt,  containing  two  units  of  water  and  one  of  potash, 
which  secures  the  requisite  acidity.11— DR.  G.  WILSON,  Edinburgh  Essays,  1856. 


90  ANSWERS    TO    PRACTICAL     QUESTIONS 

18.   Write  in  parallel  columns  the  properties  of  com- 
mon and  of  red  phosphorus. 


Common  phosphorus. 


1.  Specific  gravity— 1.83. 

2.  Burns  at  111°. 

3.  Odor  of  garlic. 

4.  Soluble  in  CS2. 

5.  Colorless,  or  straw-yellow. 

6.  A  deadly  poison. 


Amorphous  phosphorus. 


1.  Specific  gravity— 2.14. 

2.  Burns  at  500°. 

3.  Odorless. 

4.  Insoluble  in  CS3. 

5.  Brownish  red. 

6.  Harmless. 


19.  IVTiat  causes  the  difference  between  fine  and  coarse 
salt  ? 

(See  Chemistry,  p.  132.) 

The  rapidity  of  evaporation  in  the  process  of  manufacture. 

20.  WJiy  do  the  figures  in  a  glass  paper-weight  look 
larger  when  seen  from  the  top  than  from  the  bottom  ? 

The  form  of  the  glass  acts  like  a  convex  lens  to  magnify 
the  apparent  size  of  the  figures. 

21.  What  is  the  difference  between  water-slacked  and 
air-slacked  lime  ? 

The  former  is  simply  calcium  hydrate,  CaO,  H2O,  while  the 
latter  has  absorbed  both  H2O  and  CO3  from  the  air. 

22.  Why  do  oyster-shells  on  the  grate  of  a  coal-stove 
prevent  the  formation  of  clinkers  ? 

The  lime  of  the  shells  acts  as  a  flux  with  the  iron  in  the 
coal,  thus  dissolving  the  clinkers,  if  any  form. 

23.  How  is  lime-water  m,adefrom  oyster-shells  ? 

The  shells  are  burned,  driving  off  the  CO2  combined  with 
the  CaO  in  the  CaCO3,  and  the  lime  thus  formed  is  slightly 
soluble  in  water. 

24.  IVliy  do  newly  plastered  walls  remain  damp  so 
long? 

The  plaster  or  mortar  in  drying  gives  off  the  water  the 
lime  took  up  in  slacking. 


AY    POPULAR     CHEMISTRY.  91 

25.  Will  lime  lose  its  beneficial  effect  upon  a  soil  after 
frequent  applications  ? 

Lime  acts  in  various  ways  to  improve  the  fertility  of  a  soil. 
It  corrects  its  acidity,  aids  in  the  decomposition  of  the  rocky 
constituents,  hastens  the  decay  of  the  humus,  and  also  makes 
the  soil  more  -porous.  It  does  not,  however,  benefit  the  grow- 
ing plant  directly,  but  works  up  other  materials  in  the  soil.  It 
therefore  loses  its  effect  after  a  time.  The  Belgian  farmers 
have  a  proverb : 

"  Much,  lime  and  no  manure, 
Make  farm  and  farmer  poorer." 

26.  What  causes  plaster  of  Paris  to  harden  again  after 
being  moistened  ? 

(Seo  Chemistry,  p.  141.) 

It  recombines  with  water,  which  was  driven  off  in  the 
process  of  its  manufacture. 

27 •  What  is  the  difference  between  sulphate  and  sul- 
phite of  lime? 

The  former  is  a  compound  of  sulphuric  acid ;  the  latter  of 
sulphurous  acid. 

28.  What  two  classes  of  rays  are  especially  abundant 
in  the  magnesium  light  ? 

(See  Popular  Physics,  p.  243.) 

The  actinic  and  the  luminous  rays.  The  former  are  less  than 
^u^Tnr  of  an  mcn  m  length,  and  produce  chemical  change. 

29.  What  rare  metals  would  become  useful  in  the  arts 
if  the  process  of  manufacture  were  cheapened  ? 

Magnesium,  aluminum,  sodium,  etc. 

30.  Why  is  lime  placed  in  the  bottom  of  a  leach-tub  ? 

The  potash  of  the  ashes  is  generally  in  the  form  of  a  car- 
bonate, the  acid  neutralizing  in  part  the  strength  of  the  alkali. 
The  lime  combines  with  the  CO2. 

31.  Is  saleratus  a  salt  of  IL  or  of  Na? 

It  should  be  a  carbonate  of  K,  but,  on  account  of  its 
cheapness,  the  corresponding  salt  of  Na  is  often  sold  instead. 


92  ANSWERS    TO    PRACTICAL     QUESTIONS 

32.  Why  iv ill  Na  burst  into  a  Maze  wJien  thrown  on 
hot  water,  or  put  on  wetted  blotting  paper  ? 

The  oxidation  of  the  JSTa  produces  heat,  part  of  which  is 
absorbed  by  the  cold  water,  over  which  the  pellet  moves  rap- 
idly about,  so  that  the  kindling  point  of  H  i3  not  quite  reached. 
If  the  water  be  previously  heated,  or  if  the  Na  is  prevented 
from  moving  abcut,  by  resting  it  on  wetted  blotting  paper,  the 
H  from  the  H2O  is  quickly  raised  to  its  kindling  point.  It 
burns  by  taking  O  from  the  air,  and  its  flame  is  colored  yellow 
by  volatilizing  some  of  the  Na  while  the  rest  is  taking  O  from 
the  water,  and  its  hydrate  is  passing  into  solution. 

33.  Why  are  certain  Kinds  of  brick  white  ? 

They  contain  no  iron,  this  being  the  substance  which  by  its 
oxidation  gives  the  color  to  common  brick. 

34.  Illustrate  the  power  of  chemical  affinity. 

Half  the  crust  of  the  earth  is  made  up  of  oxides,  whose 
constituents  are  held  together  by  chemical  affinity.  To  separate 
the  O  from  these  elements,  with  which  it  is  united,  is  exceed- 
ingly difficult ;  so  much  so  that  the  attempt  is  but  rarely  ever 
made. 

35.  Why  does  not  a  candle  lowered  into  a  jar  of  Cl  go 
on  burning  indefinitely  ? 

The  Cl  around  it  becomes  mixed  with  HC1  fumes,  which 
stop  the  action. 

181 — 1.  Pb  is  softer  than  Fe ;  whij  is  it  not  wore 
malleable  ? 

The  facility  with  which  a  mass  of  metal  can  be  hammered 
or  rolled  into  a  thin  sheet  without  being  torn,  must  depend 
partly  upon  its  softness,  and  partly  upon  its  tenacity.  If  it 
depended  upon  softness  alone,  lead  should  be  the  most  malleable 
of  ordinary  metals ;  but,  although  it  is  easy  to  hammer  a 
mass  of  lead  into  a,  flat  plate,  or  to  squeeze  it  between  rollers, 
any  attempt  to  reduce  it  to  an  extremely  thin  sheet  fails,  from 
its  want  of  tenacity,  which  causes  it  to  be  worn  into  holes  by 
percussion  or  friction.  On  the  other  hand,  if  malleability  were 


IN    POPULAR     CHEMISTRY. 


93 


entirely  regulated  by  tenacity,  iron  would  occupy  the  first  place, 
whereas,  on  account  of  its  hardness,  it  is  the  least  malleable  of 
metals  in  ordinary  use ;  while  gold,  occupying  an  intermediate 
position  with  respect  to  tenacity,  is  the  most  malleable,  which 
appears  surprising  to  those  who  are  only  acquainted  with  gold 
in  its  ordinary  forms  of  coin  and  ornament,  in  which  it  is 
hardened  and  rendered  much  less  malleable  by  the  presence  of 
copper  and  silver. 


I.— Relative  Malleability  of  the  Metals. 

1.  Gold.  4.  Tin. 

2.  Silver.  5.  Platinum. 

3.  Copper.  6.  Lead. 

TL.— Relative  Tenacity  of  the  Metale. 


7.  Zinc. 

8.  Iron. 


Tin          

3.3 

Platinum 

l(i 

Zinc  

2 

Copper.              

18 

Palladium  

114 

Iron  

..'  27  1 

Gold... 

..12 

Steel.... 

..  42 

1.  Gold. 

2.  Silver. 

3.  Platinum. 

4.  Iron. 


III.— Relative  Ductility  of  the  Metal*. 
5.  Copper. 


6.  Palladium. 

7.  Aluminum. 


8.  Zinc. 

0.  Tin. 

10.  Lead. 

— BLOXAM. 


2.  WJiat  is  the  cause  of  the  chanf/iitfs  color  often  seen  in 
thf  scum  on  standing  ivater? 

(See  "  Interference  of  Light,1'  Popular  Physics,  p.  220.) 
The  thin  pellicles  of  iron-rust  on  standing  H8O  produce  a 
beautiful  iridescent  appearance,  the  color  changing  with  the 
thickness  of  the  oxide.  A  soap-bubble  exhibits  in  the  same  way 
a  play  of  variegated  colors  according  to  the  thickness  of  the 
film  in  different  parts. 

3.  How  can  the  spectra  of  the  metals  be  obtained  ? 

(See  Astronomy,  p.  285.) 

By  looking  through  a  prism  at  a  flame  containing  minute 
portions  of  the  volatilized  metal,  and  no  solid  particles  of  C. 

4.  Ought  cannon,  car-axles,  etc.,  to  be  nsed  until  they 
break  or  wear  out  ? 


94  ANSWERS    TO    PRACTICAL     QUESTIONS 

Cannon  are  condemned  and  recast  after  being  fired  a  cer- 
tain number  of  times,  even  though  they  show  no  flaw,  as  the 
jarring  to  which  they  are  exposed  causes  the  iron  to  take  on  a 
crystalline  form,  and  become  less  fibrous  and  tough.  A  cast- 
iron  gun  of  10-inch  bore  or  less,  ought  to  stand  1,000  rounds  ; 
larger  calibers,  a  smaller  number. 

5.  IVliy  is  "  chilled  iron"  used  for  safes  ? 

The  iron  being  cooled  so  instantaneously,  the  crystals  are 
exceedingly  small,  and  the  metal  is  correspondingly  harder  than 
when  cast  in  the  ordinary  way. 

6.  Docs    a    blacksmith   plunge    his    ivork   into    water 
merely  to  cool  it? 

The  metal  is  harder  when  cooled  quickly,  and  therefore  re- 
sists wear  longer. 

7.  What  causes  the  white  coating  made  ^vhen  we  spill 
water  on  zinc  ? 

The  oxide  of  zinc  which  is  formed  on  the  surface  of  the 
metal  through  the  favoring  influence  of  the  water. 

8.  Is  it  well  to  scald  pickles,  make  sweetmeats,  or  fry 
cakes  in  a  brass  kettle  ? 

(See  Chemistry,  p.  161.) 

9.  WJiat  danger  is  there  in  the  use  of  lead  pipes  ?    Is  a 
lining  of  Zn  or  Sit  a  protection  ? 

(See  Chemistry,  p.  162,  and  Fireside  Science,  p.  149.) 
Zinc   and  tin   are    corroded   by  oxygen,  though   less   readily 
than  Pb,  and,  while  their  salts  are  poisonous,  the  lead  is  soon 
laid  bare,  and  this  also  oxidizes. 

10.  Is  ivater  which  It  as  stood  in   a  metal-lined   ice- 
pitcher  healthful  ? 

(See  Chemistry,  p.  159.) 

The  dissimilar  metals  fastened  with  solder,  which  corrodes 

in    the  presence    of    water,    develop   a   voltaic    current  which, 

hastens  the   oxidation.     The  salts  thus   formed   are   very  dan 
gerous. 


IN    POPULAR     CHEMISTRY.  95 

11.  If  yon  ask  for  "  cobalt"  at  a  drug-store,  tvhat  will 
you  get?    If  for  "arsenic"? 

Impure  metallic  arsenic  is  sold  as  "cobalt,"  while  arsenious 
anhydride  is  called  "arsenic." 

12.  What  two  elements  are  fluid  at  ordinary  tempera- 
tures ? 

Bromine  and  mercury. 

13.  Should  we  touch  a  gold  ring  to  mercury  ? 

The  mercury  will  form  with  the  gold  an  amalgam. 

14.  Wliy  does  silver  blacken  if  handled  ? 

The  perspiration  of  the  body  contains  S,  which  combining 
with  the  metal  forms  silver  sulphide,  which  is  black. 

15.  IVIiy  does  silver  tarnish  rapidly  where  coal  is  used 
for  fires  ? 

S,  which  is  present  in  coal,  forms  a  silver  sulphide. 

16.  Why  is  a  solution  of  coin  blue  ? 

From  the  Cu  which  is  contained  in  silver  coin  forming  Ou 
(NO3)2,  which  is  blue. 

17.  MTIiy  will  a  solution  of  silver  nitrate  curdle  brine  ? 

A  white,  curdy  precipitate  of  silver  chloride  is  formed. 

18.  Wliy  does  writing  with  indelible  ink  turn  black 
when  exposed  to  the  sun,  or  to  a  hot  iron  ? 

By  the  decomposition  of  the  silver  salt  contained  in  the 
ink,  and  consequent  production  of  Ag2O,  which  stains  organic 
matter  black. 

19.   What  alloys  resemble  gold  ? 

Oroide,  aluminum-bronze,  etc. 

2O.  WJiy  does  a  fish-hook  "  rust  out"  the  line  to  which 
it  is  fastened  ? 

Ferric  oxide  and  ferric  hydrate  act  as  conveyers  of  O,  ab- 
sorbing it  from  the  air  and  giving  it  up  to  organic  bodies  with 
which  they  are  in  contact. 


96  ANSWERS    TO    PRACTICAL     QUESTIONS 

21.  Why  do  the  nails  in  clap-boards  loosen  ? 

See  Question  20. 

22.  Show  that  the  earth's  crust  is  mainly  composed  of 

burnt  metals. 

(See  Cooke's  Religion  and  Chemistry.) 

It  consists  largely  of  potassium,  magnesium,  calcium,  alu- 
minum, sodium,  etc.,  in  combination  with  O.  These  compounds 
are  the  products  of  combustion. 

The  elements  O,  Si,  Al,  Mg,  Ca,  K,  Na,  Fe,  C,  S,  H,  Cl, 
and  N — 13  in  all — probably  make  up  T9^  of  the  earth's  crust. 

23.  What  kind  of  iron  is  used  for  a  magnet  ?    For  a 
magnetic  needle  ? 

Steel  for  a  permanent  magnet,  and  therefore  for  a  magnetic 
needle  ;  pure  soft  iron  for  an  electro-magnet. 

24.  Why  does  a  "tin"  pail  so  quickly  rust  out  when 
once  the  tin  is  worn  through  ? 

These  pails  are  made  of  sheet  iron,  which  is  covered  with  a 
coating  of  tin,  which  causes  the  popular  name  for  them.  If 
this  is  scratched  through,  the  iron  and  tin  in  contact  are  ex- 
posed to  the  water  ;  voltaic  action  is  started,  and  the  iron  rap- 
idly rusts. 

25.  Wlty  is  the  zinc  oacide  found  in  Neiv  Jersey  red9 
when  zinc  rust  is  white  ? 

The  oxide  in  New  Jersey  is  colored  by  compounds  of  iron 
and  manganese. 

26.  Should  we  filter  a  solution  of  permanganate  of 
potash  through  paper  ? 

(See  Chemistry,  p.  157,  note.) 
No.    The  salt  will  give  up  O  and  corrode  the  filter. 

27 •  Why  is  woody  cordage,  etc.,  sometimes  soaked  in  a 
solution  of  corrosive  sublimate  ? 

This  salt  possesses  strong  antiseptic  properties. 

28.  Why  does  the  ivhite  paint  around  a  sink  turn 
black? 


IN    POPULAR    CHEMISTRY.  97 

H2S  is  set  free,  which,  acting  on  the  paint,  forms  lead  sul- 
phide, which  is  black. 

29.  Why  is  aluminum,  rather  than  platinum,  used  for 
making  the  smallest  weights  ? 

Because  of  its  low  specific  gravity  as  compared  with  that 
of  platinum. 

30.  How  would  you  detect  the  presence  of  iron  particles 
in  Mack  sand  ? 

By  a  magnet. 

31.  Which  metals  can  be  welded  ? 

Iron  and  platinum,  most  easily  ;  others  also  by  using  a  pow- 
erful electric  current  to  heat  the  ends  of  the  pieces  of  metal. 

32.  When  the  glassy  slag  from  a  blast-furnace  has  a 
dark  color,  ^vhat  does  it  show  ? 

It  might  be  anticipated  that  the  appearance  of  the  slag 
would  convey  to  the  experienced  eye  some  useful  information 
with  respect  to  the  character  of  the  ore  and  the  general  prog- 
ress of  the  smelting  operation.  A  good  slag  is  liquid,  nearly 
transparent,  of  a  light-gray  color,  and  has  a  fracture  somewhat 
resembling  that  of  limestone.  A  dark  slag  shows  that  much 
of  the  oxide  of  iron  is  escaping  unreduced.  Streaks  of  blue 
are  commonly  found  when  ores  containing  sulphur  are  being 
smelted,  possibly  from  the  presence  of  a  substance  similar  to 
ultramarine,  the  constituents  of  which  are  all  present  in  the 
slag.  Again,  the  slags  obtained  in  smelting  ores  containing 
titanium  generally  present  a  peculiar  blistered  appearance. — 
BLOXAM. 

33.  In  welding  iron  the  surfaces  to  be  joined  are  some- 
times sprinkled  with  sand.    Explain. 

The  silica  acts  as  a  flux  with  the  oxide  upon  the  surface, 
and  lays  bare  the  metal  for  welding. 

34.  Wliat  is  the   difference  between   an  alloy  and  an 
amalgam  ? 

An  amalgam  is  composed  of  mercury  and  some  other 
metal.  An  alloy  consists  of  any  metals  whatever. 


98  ANSWERS    TO    PRACTICAL     QUESTIONS 

35.  Steel  articles  (ire  blued  to  protect  from  rusting,  by 
heating  in  a  sand-bath.    Explain. 

A  thin  coating  of  oxide  is  formed  on  the  surface  of  the 
metal. 

36.  Give  the  formulas  for  copperas  and  white  lead. 

1.  FeSO4  =  FeO,SO3. 

2.  PbCO3  =  PbO,C03. 

37.  Why  is  Hg  used  for  filling  thermometers  ? 

Because  it  is  fluid  at  all  ordinary  temperatures. 

38.  What  oxides  are  formed  by  the  combustion  of  Na9 
K,  Zn,  8,  Fe,  Pb,  Cti,  P,  etc.  ?     Which  are  bases  ?    Anhy- 
drides ?    Give  the  common  name  of  each. 

(1.)  Na2O  is  formed  when  ISTa  oxidizes  in  dry  air,  or  oxy- 
gen at  a  low  temperature.  This  takes  up  water  with  great 
avidity,  forming  HNaO  (NaHO),  sodium  hydroxide.  Na2O2  is 
made  when  Na  is  heated  to  200°  C.  HNaO  is.  the  caustic  soda 
of  commerce,  and  is  an  alkaline  base. 

(2.)  K  in  a  similar  manner,  depending  upon  the  tempera- 
ture, forms  K2O,  K2O2,  and  K2O4.  The  first,  with  water, 
forms  the  ordinary  caustic  potash,  HKO,  of  commerce.  It  is 
an  alkaline  base. 

(3.)  ZnO  is  the  only  known  oxide  of  zinc.     It  forms  salts. 

(4.)  Seven  compounds  of  S  and  O  are  known,  but  only  two 
are  of  interest — the  familiar  anhydrides,  SO2  and  SO3. 

(5.)  The  oxides  of  iron  are  four  in  number  :  (1)  the  mon- 
oxide, or  ferrous  oxide,  FeO,  from  which  the  green  ferrous  salts 
are  derived  ;  (2)  the  sesquioxide,  or  ferric  oxide,  Fe2O3,  yield- 
ing the  yellow  ferric  salts;  (3)  the  magnetic  or  black  oxide, 
Fe3O4,  which  does  not  form  any  definite  salts ;  (4)  ferric  acid, 
H2FeO4,  a  weak  acid,  forming  colored  salts  with  potassium. 

(6.)  Pb  forms  two  oxides,  the  monoxide  and  the  dioxide. 
The  former  is  the  well-known  litharge,  which  is  the  base  of 
the  lead  salts. 

(7.)  Cu  has  two  oxides  — the  cuprous  (CuaO)  and  cupric 
(CuO),  both  of  which  form  salts,  thus  giving  rise  to  two  series, 


IN    POPULAR     CHEMISTRY.  99 

the  cuprous    and   the  cupric  salts.     The   two  oxides  are  com- 
monly known  as  the  red  and  the  black. 

(8.)  Phosphorus  forms  two  oxides,  phosphorous  anhydride 
(P2O3)  and  phosphoric  anhydride  (P2O5). 

39.  Is  charcoal  lighter  than  H2  O  ? 

Charcoal  appears  at  first  sight  to  be  lighter  than  water,  as 
a  piece  of  it  floats  on  the  surface  of  this  liquid  ;  this  is,  how- 
ever, due  to  the  porous  nature  of  the  charcoal,  for  if  it  be 
finely  powdered  it  sinks  to  the  bottom  of  the  water.  —  ROSCOE. 

40.  Name  the.vitriols. 

The  compounds  of  sulphuric  acid,  commonly  called  "the 
vitriols,"  are  as  follows: 

1.  Sulphate  of  iron,  Green  vitriol. 

2.  Sulphate  of  copper,  Blue  vitriol. 

3.  Sulphate  of  zinc,  White  vitriol. 

41.  Is  My  univalent  or  bivalent  ?    Zn  ? 

Mg  belongs  to  the  zinc  class  of  metals  which  comprises 
magnesium,  zinc,  cadmium,  and  indium.  These  are  all  bivalent. 

42.  Name  some  dibasic  acid. 

Sulphuric  acid. 

43.  Name  a  neutral  salt.    An  acid  salt. 

Sodium  sulphate  is  neutral  (Na2SO4).  Hydro-sodium  sul- 
phate is  acid  (HNaSOJ. 

44.  Calculate    the  percentage  of  water    contained  in 
crystallized  copper  sulphate.    Sodium  sulphate.    Calcium 
sulphate.    Alum. 

(1.)  CuSO4,  5H3O  =  249.5. 
5H20  =  90. 

Hence,        -£$%  =  .36  =  36  %  of  copper  sulphate  is  water. 


(2.)  Na2SO4,  10H2O  =  322. 
10H2O  =  180. 

Hence,        iff  =  .55  =  55  %  of  sodium  sulphate  is  water, 


100  ANSWERS    TO    PRACTICAL    QUESTIONS 

(3.)  CaSO4,  2H2O  =  172, 

'2H2O  =  36. 
Hence,  -^  =  .20  =  20  %  of  gypsum  is  water. 

(4.)  A12K2,  4SO4  +24H2O  =  949. 
24H2O  =  432. 
Hence,  $ff  =  .45  —  45  %  of  potash  alum  is  water. 

45.   What  is  the  test  for  Ay  ?     Ca  ? 

Ag  can  be  easily  detected  when  in  solution  by  the  precipi- 
tation of  the  white,  curdy  chloride,  insoluble  in  H2O  and 
HNO3,  and  soluble  in  H3N  :  the  metal  can  be  obtained  in 
malleable  globules  before  the  blowpipe,  and  is  reduced  from  its 
solutions  by  Fe,  Cu,  P,  and  Hg.  Ag  is  estimated  quantita- 
tively either  as  the  chloride  or  as  the  metal. 

Copper  may  be  tested  (1)  by  the  black  insoluble  sulphide  ; 
(2)  by  the  blue  hydrate  turning  black  on  heating  ;  (3)  by  the 
deep-blue  coloration  with  ammonia  ;  (4)  by  the  deposition  of 
red  metallic  copper  upon  a  bright  surface  of  iron  placed  in  the 
solution. 

40.  What  weight  of  crystallized  "tin  salts"  (SnCl2, 
2H2  O)  can  be  prepared  from  one  ton  of  metallic  tin  ? 

Sn  :  SnCl2,  2H3O  :  :  2,000  Ibs.  :  x. 
118  :  225  ::  2,000  Ibs.  :  x. 

118  x  =  450,000  Ibs. 

x  =  3813.56  Ibs.  (SnCU,  2H2O). 

47.  1OO  parts  by  weight  of  silver  yield  132.87  parts  of 
silver  chloride.  Given  the  atomic  iveiyht  of  chlorine  (35.4], 
required  that  of  silver. 

32.87  :  100  :  :  35.4  :  x. 


48.   What  is  the  composition  of  slacked  lime  ? 

(See  Chemistry,  p.  139.) 
OaO,H20. 

49.  How  is  ferrous  sulphate  obtained?     How  many 
tons  of  crystals  can  be  obtained  by  the  slow  oxidation  of 


IN    POPULAR     CHEMISTRY. 


101 


23O  tons    of  iron  pyrites    containing  37.5  per  cent,  of 

sulphur  ? 

(See  Cfiemistry,  p.  158.) 

3?i  %  of  230  =  86.25  tons,  the  weight  of  S  contained  in  the 
pyrites. 

S  :  FeSO4,  7H2O  :  :  86.25  :  x. 

32:  278  ::  86.25  :  x. 

x  =  749.296  tons  of  FeSO4,  7H2O. 

50.  Required  5OO  tons  of  soda  crystals;  what  will°be 
the  weight  of  salt  and  pure  sulphuric  acid  needed  ? 

Find  (1)  how  much  Na  there  is  in  500  tons  of  "soda,"  and 
(2)  how  much  NaCl  would  be  needed  to  furnish  that  amount  of 
the  metal  in  case  all  were  utilized. 

(1.)  Na2  :  Na2CO3,  10H2O  : :  x  :  500  tons. 
46  :  286  :  :  x  :  500  tons. 

286  x  —  23,000  tons. 

x  =  80.42  -  tons  (Na). 

(2.)  Iff  of  any  amount  of  NaCl  is  Na  ;  hence,  to  furnish 
80.42  tons  of  Na  would  require  ff|x80.42  tons  =  204.546  tons 
(Nad). 

(3.)  By  comparing  the  atomic  weights  of  the  substances,  it 
will  be  seen  that  for  46  parts  of  Na  there  must  be  98  of  pure 
H2SO4.  ft  x  204.546  tons  =  435.771  tons  (H2SO4). 

51.  Describe  the  uses  of  lime  in  agriculture. 

Lime  acts  in  various  ways  to  improve  the  fertility  of  a  soil. 
It  corrects  its  acidity,  aids  in  the  decomposition  of  the  rocky 
constituents,  hastens  the  decay  of  the  humus,  and  also  makes 
the  soil  more  porous.  It  does  not,  however,  benefit  the  grow- 
ing plant  directly,  but  works  up  other  materials  in  the  soil.  It 
therefore  loses  its  effect  after  a  time. 

52.  Hoiv  many  tons  of  oil  of  vitriol,  containing  7O  per 
cent,  of  pure  acid  (Jf2£O4),  can  be  prepared  from  25O  tons 
of  iron  pyrites,  containing  42  per  cent,  of  sulphur  ? 

(1.)  (See  Question  49.)    250  tons  x. 42  =  105  tons  (S). 
(2.)  S  :  H3SO4  : :  105  tons  :  x. 
32  :      98      : :  105  tons  :  x. 
32  x  =  10,290  tons. 

x  =  321.56  tons  (H8SO4). 


102  ANSWERS    TO    PRACTICAL     QUESTIONS 

(3.)  If  321.56  tons  (H2SO4)  is  70  %  of  the  given  oil  of  vit- 
riol, the  entire  amount  would  be  321.56  tons  x  -^  =  459.28  tons 
(oil  of  vitriol). 

247 — 1.  Hoiv  would  you  prove  the  presence  of  tannin 
in  tea  ? 

By  adding  a  few  drops  of  a  solution  of  ferrous  sulphate. 
This  would  form  a  dark  precipitate  of  iron  tannate. 

2.  How  would  you  test  for  Fe  in  a  solution  ? 

(See  MUler's  Inorganic  Chemistry,  p.  625.) 

A  solution  of  nutgalls  will  give  a  bluish-black,  inky  precipi- 
tate. The  ferrous-  or  proto-salts  are  distinguished  by  their  light 
green  color,  and  by  their  solutions  giving  (1)  a  white  precipi- 
tate, with  caustic  alkalies ;  (2)  a  light  blue  precipitate,  with  po- 
tassium ferrocyanide,  which  rapidly  becomes  dark;  while  the 
ferric-  or  per-salts  are  yellow-colored,  and  their  solutions  yield 
(1)  a  deep  reddish-brown  precipitate,  with  the  caustic  alkalies ; 
and  (2)  a  deep-blue  precipitate  (Prussian  blue),  with  potassium 
ferrocyanide. 

3.  Why  can  we  settle  coffee  with  an  egg  ? 

The  albumen  of  the  egg  coagulates  by  heat,  and,  entan- 
gling the  particles  of  coffee,  mechanically  carries  them  to  the 
bottom. 

4.  How  would  you  show  the  presence  of  starch  in  a 
potato  ? 

A  solution  of  iodine  will  form  the  blue  iodide  of  starch. 

5.  IVJiy  is  starch  stored  in  the  seed  of  a  plant? 

For  the  growth  of  the  young  plant. 

6*.   Why  are  unbleached  cotton  goods  dark-colored  ? 

Because  of  the  dirt  gathered  in  the  process  of  manufacture. 
The  cotton  balls  are  snowy  white. 

7.  Why  do  beans,  rice,  etc.9  swell  when  cooked  ? 

On  account  of  the  bursting  of  the  starch  granules. 

8,  Wliy  does  decaying  wood  darken  ? 


IN   POPULAR     CHEMISTRY.  103 

On  account  of  the  formation  of  humus,  which  contains  car- 
bon in  excess. 

9.  How  would  you  show  that  C  exists  in  sugar  ? 

By  heating  it  until  the  H  and  O  are  all  driven  off.  A  mass 
of  porous  charcoal  remains  on  the  plate. 

1O.  Whyr  do  fruits  lose  their  sweetness  when  over-ripe  ? 

(See  Miller's  Organic  Chemistry,  p.  875.) 

The  vegetable  acid  contained  in  the  fruit  when  green,  oxi- 
dizes as  the  ripening  process  continues,  O  being  absorbed,  and 
CO3  evolved.  If  this  continues  too  long,  the  sugar  itself  be- 
comes oxidized. 

11.  Why  does  maple-sap  lose  its  sweetness  when  the  leaf 
starts  ? 

The  sugar  of  the  sap  is  applied  to  the  wants  of  the  grow- 
ing tree. 

12.  Should  yeast-cakes  be  allowed  to  freeze? 

A  cold  of  32°  will  kill  the  ferment. 

13.  Why  will  ivine  sour  if  the  bottle  be  not  well  corked  ? 

The  presence  of  air  will  cause  the  continuation  of  the  oxi- 
dizing process  into  the  second  or  acetic  stage. 

14.  W7iy  can  vinegar  be  made  from  sweetened  water 
and  brown  paper  ? 

The  paper  acts  as  a  ferment,  while  the  sugar  or  molasses  is 
oxidized  into  alcohol,  and  thence  into  acetic  acid. 

15.  Why  should  the  vinegar-barrel  be  kept  in  a  warm 
place  ? 

Fermentation  takes  place  to  the  best  advantage  at  a  special 
temperature,  about  70°  F. 

16.  Why   does    "scalding"  check  the    "working"  of 
preserves  ? 

The  ferment  which  causes  the  fermentation  is  killed  by  the 
heat. 


104  ANSWERS    TO    PRACTICAL     QUESTION'S 

1 7.  Is  the  oxalic  acid  in  the  pie-plant  poisonous  ? 

It  is  neutralized  by  the  alkaline  base,  with  which  it  is  com- 
bined in  the  plant. 

18.  How  may  ink-stains  be  removed  ? 

By  a  solution  of  oxalic  acid,  forming  an  iron  oxalate  which 
is  soluble  in  water,  and  hence  may  be  washed  out. 

W.   Wliy  is  leather  black  on  only  one  side  ? 

The  solution  of  copperas,  which  blackens  the  leather,  is  ap- 
plied on  only  one  side. 

20.  JfJiy  do  drops  of  tea  stain  a  knife-blade  ? 

The  tannic  acid  of  the  tea  combines  with  the  iron,  forming 
an  iron  tannate.* 

21.  Why  will  not  coffee  stain  it  in  the  same  way  ? 

(See  Miller's  Organic  Chemistry,  p.  549.) 

The  modification  of  tannin  contained  in  coffee,  unlike  that 
in  tea,  turns  a  solution  of  ferrous  sulphate  green,  and  will  not 
precipitate  one  of  gelatin. 

22.  Why  does  ivriting-fluid  darken  oti  exposure  to  the 
air? 

It  absorbs  O,  the  iron  changing  to  ferric  oxide. 

23.  IfJiat  causes  the  disagreeable  smell  of  a  smolder- 
ing ^vick  ? 

A  volatile  substance,  termed  acrolein,  is  produced  in  the  de- 
composition of  the  oil. 

24.  IVJiy  does  ink  corrode  steel  pens  ? 

The  free  sulphuric  acid  of  the  ink  combines  with  the  iron 
of  the  pen. 

*  The  tannic  acid  of  the  tea  tans  the  albumen  of  the  milk  used  in 
seasoning  the  tea,  forming  flakes  of  real  leather.  It  has  been  calculated 
that  an  average  tea-drinker,  in  this  way,  makes  and  drinks  enough  leather 
each  year  to  make  a  pair  of  shoes.  The  albumen  of  milk  uniting  with  the 
tannic  acid  of  tea,  softens  its  flavor.  This  is  generally  preferred  to  the 
harsh,  clear  beverage. 


IN    POPULAR     CHEMISTRY.  105 

25.  How   does  a  bird   obtain  the   CaCO3  for   its  egg 

shells  ? 

(See  chemistry  of  a  lien's  egg  in  Fireside  Science.) 

A  common  hen's  egg  is  95  per  cent,  carbonate  of  lime,  one 
per  cent,  phosphate  of  lime  and  magnesia,  and  two  per  cent, 
animal  matter.  The  shell  would  weigh  over  100  grains,  so  that 
a  hen  laying  100  eggs  in  a  season  would  require  nearly  1^  Ibs. 
of  CaCO3.  The  hen  must  in  part  secrete  this  from  her  food, 
and  in  part  gather  it  from  the  sand,  pebbles,  etc.,  she  picks  up 
amid  her  incessant  scratching  and  searching. 

26.  Why  does  new  soap  act  on  the  hands  more  than 
old  ? 

The  spent  lye,  which  contains  the  excess  of  alkali,  gradu- 
ally separates  from  the  soap,  leaving  only  the  salts  in  which 
the  alkali  is  neutralized  by  the  fatty  acids.  Also  a  more  com- 
plete combination  takes  place,  whereby  some  free  alkali  is 
taken  up  by  the  acids,  perhaps  before  uncombined.  The  for- 
mer statement  is  especially  true  in  the  case  of  soft  or  home- 
made soap. 

27.  What  is  the  shiny  coat  on  certain  leaves  and  fruits  ? 

A  species  of  wax  secreted  by  the  plant. 

28.  Why  does  tiwpentine  burn  with  so  much,  smoke  ? 

Because  it  contains  an  excess  of  carbon. 

20.   Wliy  is  the  nozzle  of  a  turpentine  bottle  so  sticky  ? 

The  turpentine  on  exposure  to  the  air  oxidizes,  turning  to 
rosin. 

30.  Why  does  kerosene  give  more  light  than  alcohol  ? 

It  contains  more  carbon,  which,  when  heated  in  the  flame 
of  the  burning  H,  gives  out  a  white  light. 

31.  IVliat  is  the  antidote  to  oxalic  acid  ?     Why  ? 

Magnesia  or  chalk,  forming  an  insoluble  oxalate. 

32.  Would  you  iveaken  camphor  spirits  with  ivater  ? 


106  ANSWERS    TO    PRACTICAL     QUESTIONS. 

No ;  since  camphor  is  insoluble  in  dilute  alcohol.  The  prin- 
ciple is  the  same  as  that  of  the  precipitation  of  lead  from 
dilute  sulphuric  acid. 

35.  What  is  the  difference  between  rosin  and  resin  ? 

Rosin  is  an  oxidized  resin.  Rosin  is  a  species,  and  resin  a 
genus. 

34.  IVJiy  does   skim -milk   look  blue    and   new  milk 
white  ? 

The  globules  of  butter  contained  in  new  milk  reflect  the 
light,  and  so  make  it  look  white ;  but  when  they  are  removed, 
by  the  separation  of  the  cream,  more  light  is  transmitted,  and 
only  the  blue  is  reflected  to  the  eye. 

35.  Wliy  does  an  ink-spot  turn  yellow  after  washing 
with  soap  ? 

The  free  alkali  of  the  soap  combines  with  the  tannic  acid 
of  the  ink,  leaving  the  oxide  of  iron  (ferric  oxide),  which  stains 
the  cloth  yellow. 


ANSWERS 


TO  THE 


QUESTIONS 


IN  THE 

NEW  DESCRIPTIVE  ASTRONOMY. 

32.  —  1.  Hotv  high  is  the  North  Star  above  your  hori- 

zon? 

(See  Astronomy,  p.  218.) 

It  should  be  remembered  that  the  North  Star  revolves 
around  the  true  North  Pole  at  a  distance  of  about  1£°  ;  hence 
it  marks  the  exact  height  of  the  Pole  above  the  horizon  only 
twice  in  twenty-four  hours. 

2.  What  is  the  sun's  right  ascension  at  the  autumnal 
equinox  ?    At  the  vernal  equinox  ? 

At  the  vernal  equinox,  the  sun  is  in  Aries,  and  its  R.  A.=0. 
At  the  autumnal  equinox,  it  is  in  Libra,  and  its  R.  A.  =  180°. 

3.  What  ^vas  the  first  discovery  made  by  the  telescope  ? 

(See  Astronomy,  p.  20  ;  articles  in  Appletons1  Cyclopedia  on  Telescope 
and  Gt-alileo  ;  and,  also,  Routledge's  History  of  Science,  p.  107.) 

Galileo's  telescope  was  constructed  on  the  principle  of  an 
opera-glass. 

4.  How  high  above  the  horizon  of  any  place  are  the 
equinoctial  points  when  they  pass  the  meridian  ? 

(See  Astronomy,  note,  p.  27.) 
The  co-latitude  of  the  place. 

5.  Jupiter  revolves  around  the  sun  in  12  of  our  years. 
Assuming  the  earth's  distance  from  the  sun  to  be  93,OOO,- 
OOO  miles  9  compute  Jupiter's  distance  by  applying  Kep- 
ler's third  law. 

(See  Astronomy,  note,  p.  19.) 


108  ANSWERS    TO    PRACTICAL     QUESTIONS 

If  we  square  the  period  of  any  planet,  expressed  in  years, 
and  extract  the  cube  root  of  this  product,  the  result  will  be  the 
mean  distance  from  the  sun,  expressed  in  astronomical  units, 
i.e.,  in  radii  of  the  earth's  orbit.  Jupiter's  period  of  12  years 
will  give  a  result  of  5.2028.  93,000,000  miles  x  5.2028  =  483,- 
860,400  miles. 

6.  The  latitude  of  Albany  is  42°  39'  N. ;  what  is  the 
sun's  meridian  altitude  at  that  place  ivJien  it  is  in  the  celes- 
tial equator  ? 

(See  Astronomy,  note,  p.  27.) 

90°- 42°  39'=  47°  21'. 

7.  Wliat  is  the  co-latitude  of  a  place  ? 

(See  Astronomy,  note,  p.  27.) 

The  co-latitude  is  the  complement  of  the  latitude. 

8.  Wliafis  the  declination  of  the  zenith  of  the  place  in 
which  you  reside  ? 

(See  Astronomy,  note,  p.  27.) 

It  equals  the  latitude. 

.9.   Why  are  the  stars  generally  invisible  by  day  ? 

(See  Astronomy,  p.  25.) 

The  stars  would  be  visible  in  the  day-time  if  it  were  not  for 
the  atmosphere.  Compare  the  description  of  a  lunar  sky,  on 
page  134  of  the  Astronomy. 

10.  Why  is  the  ecliptic  so  called  ? 

(See  Astronomy,  note,  p.  58.) 

11.  Who  first  taught  that  the  earth  is  round  ? 

The  discovery  of  the  rotundity  of  the  earth  has  been  as- 
cribed to  Thales ;  others  attribute  it  to  Aristotle. 

12.  IVliat  is  Astrology  ? 

A  magic  art  that  pretends  to  foretell  events  by  means  of 
the  stars. 

13.  How  can  ive  distinguish  the  fixed  stars  from  the 

planets  ? 

(See  Astronomy,  pp.  2  and  203.) 


IN    DESCRIPTIVE    ASTRONOMY.  109 

14.  How  long  ivas  the  Ptolemaic  system  accepted? 

It  was  taught  in  the  schools  for  about  1400  years,  or  until 
the  time  of  Galileo— the  17th  century. 

15.  In  ivhat  respect  did  the  Copernican  system,  differ 
from  the  one  now  received  ? 

(See  Astronomy,  p.  14.) 

10.  For  what  is  Astronomy  indebted  to  Galileo?  To 
Neivton  ? 

Galileo  discovered  the  structure  of  the  moon ;  the  existence 
of  Jupiter's  moons  and  their  revolution  around  their  primary ; 
the  stars  of  the  milky  way  ;  and  the  rotation  of  the  sun  on 
its  axis  (as  proved  by  the  appearance  of  the  spots).  Newton 
discovered  the  law  of  gravitation,  and  by  means  of  it  explained 
the  specific  gravity  of  the  planets,  the  cause  of  the  tides,  the 
shape  of  the  earth,  the  theory  of  precession  of  the  equinoxes, 
and  the  paths  of  the  comets.  Bead  Brewster's  Life  of  Newton; 
also,  Buckley's  History  of  Natural  Science. 

17.  What  is  the  amount  of  the  obliquity  of  the  ecliptic  ? 

(See  Astronomy,  p.  29.) 

18.  Define  Zenith.    Nadir.    Azimuth.    Altitude.    Equi- 
noctial.   Right  Ascension.    Declination.    Equinox.    Eclip- 
tic.    Colure.     Solstice.    Polar  distance.     Zenith  distance. 
The  Zodiacs 

These  terms  are  defined  under  the  various  subjects  on  pp. 
26-30  of  the  Astronomy. 

IV.  If  the  H.A.of  the  sun  be  8O\  state  in  ^vhat  sign  he 
is  then  located.  16O°.  28O°. 

(See  Astronomy,  table  on  p.  31.) 

1  sign  =  30°.  80°  would  locate  the  sun  in  Gemini ;  160°,  in 
Virgo  ;  280°,  in  Capricornus. 

2O.  Why  does  the  angle  which  the  ecliptic  makes  with 
the  horizon  vary  ? 

(See  Astronomy,  p.  29.) 

The  angle  between  the  horizon  and  the  celestial  equator  is 
constant ;  the  ecliptic  being  oblique  to  the  equator,  the  angle 
that  it  makes  with  the  horizon  must  vary  as  it  revolves. 


110  ANSWERS    TO    PRACTICAL     QUESTIONS 

21.  W7iy  is  the  angle  which  the  celestial  equator  makes 
with  the  horizon  constant  ? 

(See  Astronomy,  p.  29.) 

The  celestial  equator  is  perpendicular  to  the  axis  of  the 
heavens,  and  hence  all  parts  of  it  make  the  same  angle  with 
the  celestial  axis  and  with  the  horizon. 

I  98 — 1.   Would  the  earth  rise  and  set  to  a  Lunarian  ? 

(See  Astronomy,  p.  134.) 

The  earth  would  not  rise  or  set,  as  the  moon  does  with  us, 
but  would  merely  oscillate  to  and  fro  through  a  few  degrees. 
A  Lunarian  would  see  the  earth  constantly  in  the  sky,  under- 
going all  the  phases  the  moon  presents  to  the  earth.  But  when 
it  is  full  moon  to  us,  it  is  new  earth  on  the  moon.  During  the 
first  and  last  quarters,  the  changes  would  occur  during  the  day- 
time ;  during  the  second  and  third,  in  the  night.  The  rapid 
rotation  of  the  earth,  repeated  fifteen  times  during  a  lunar 
night,  must  greatly  diversify  the  appearance  of  the  earth. — See 
Olmstead's  Letters  on  Astronomy,  p.  180. 

2.  Could  there  be  a  transit  of  Jupiter  ? 

(See  Astronomy,  p.  67.) 

No.    Jupiter  is  a  superior  planet. 

3.   IVliy  does  Mars'  inner-moon  rise  in  the  west  ? 

(See  Astronomy,  note  on  p.  153.) 

This  satellite  performs  a  revolution  in  its  orbit  in  less  than 
half  the  time  that  Mars  revolves  on  its  axis.  In  consequence, 
to  the  inhabitants  of  Mars,  it  would  seem  to  rise  in  the  west 
and  set  in  the  east.  The  revolution  of  the  moon  around  the 
earth  and  of  the  earth  on  its  axis,  are  both  from  west  to  east ; 
but,  the  latter  revolution  being  the  more  rapid,  the  apparent 
diurnal  motion  of  the  moon  is  from  east  to  west.  In  the  case 
of  the  inner  satellite  of  Mars,  however,  this  is  reversed,  and  it 
therefore  appears  to  move  in  the  actual  direction  of  its  orbital 
motion.  The  rapidity  of  its  phases  is  also  equally  remarkable. 
It  is  less  than  two  hours  from  new  moon  to  first  quarter. — New- 
comb  and  Holden's  Astronomy,  p.  339. 


IN    DESCRIPTIVE    ASTRONOMY.  Ill 

4.  In  wJiat  part  of  the  ski/  do  you  always  look  for  the 
planets  ? 

Within  the  limits  of  the  Zodiac.  A  few  of  the  asteroids 
only  pass  outside  this  belt  of  the  heavens. 

.5.  Show  how  it  was  impossible  for  the  darkness  that 
occurred  at  the  time  of  the  Crucifixion  of  Christ  to  have 
been  caused  by  an  eclipse  of  the  sun. 

The  Feast  of  the  Passover  took  place  at  full  moon.  "With 
the  Jews,  a  month  began  when  the  new  moon  was  seen.  Per- 
sons were  appointed  to  watch,  about  the  time  it  was  expected, 
on  the  tops  of  mountains.  As  soon  as  they  saw  its  light,  they 
gave  notice  by  sounding  trumpets  and  building  fires." — Kevin's 
Biblical  Antiquities. 

0.  Is  there  any  danger  of  a  collision  between  the  earth 

and  a  comet  ? 

(See  Astronomy,  p  192.) 

A  collision  between  the  earth  and  a  comet  must  be  a  rare 
occurrence.  Babinet  computed  that  one  would  strike  the  earth, 
on  the  average,  every  15,000,000  years.  There  are  certainly, 
however,  comets  whose  orbits  cross  the  earth's  path,  and  if  we 
should  happen  to  reach  the  crossing  at  the  same  time  with  one 
of  them,  there  would  be  a  collision.  We  should  probably  never 
know  of  the  event  unless  we  were  watching  for  it. 

7.  Hoiv  are  aerolites  distinguished  ? 

(See  Astronomy,  pp.  177,  178.) 

Aerolites,  when  found,  generally  have  an  exterior  crust  of 
fused  material,  presenting  a  glossy,  pitch-like  appearance.  An 
analysis  of  the  interior  commonly  presents  a  combination  of 
elements  that  is  so  characteristic  as  to  identify  the  body  as  an 
aerolite  even  when  not  seen  to  fall.  Large  masses  have  been 
found  in  Northern  Mexico  which  are  thus  known  to  be  of  me- 
teoric origin. 

"  The  meteoric  stones  may  be  divided  into  two  distinct 
groups — meteoric  iron,  and  meteoric  stones  proper. 

"  1.  Meteoric  iron  is  an  alloy  of  iron  and  nickel,  containing 
about  10  per  cent,  of  nickel,  and  small  quantities  of  cobalt, 


112  ANSWERS    TO    PRACTICAL     QUESTIONS 

manganese,  magnesium,  tin,  copper,  and  carbon.     This  alloy  has 
not  been  found  among  terrestrial  minerals. 

"  2.  The  meteoric  stones  proper  are  composed  of  minerals 
of  volcanic  origin,  and  such  as  are  found  abundantly  in  terres- 
trial lavas  and  trap-rocks,  viz.  : 

Magnetic  iron,  Olivine, 

Sphene,  Anorthite, 

Chrome  iron,  Labradorite, 

Apatite  (?),  Augite, 

together  with  a  varying   proportion    of  the  meteoric  iron-nickel 
alloy." — Haughton's  Astronomy. 

8.  When  do  ive  see  the  old  moon  in  the  ivest  after  sun- 
rise ? 

(See  Astronomy,  p.  127.) 

.9.  When  do  we  see  the  moon  high  in  the  eastern  sky  in 
the  afternoon  before  the  sun  sets  ? 

(See  Astronomy,  p.  127.) 

During  the  second  quarter,  before  she  comes  into  opposition. 

10.  When  is  a  planet  morning,  and  when    evening, 

star  ? 

(See  Astronomy,  pp.  65,  70.) 

11.  Is  the  sun  really  hotter  in  summer  than  in  ^vinter  ? 

(See  Astronomy,  p.  101.) 

12.  IVliy  is  a  planet  invisible  at  conjunction  ? 

(See  Astronomy,  p.  65.) 

13.  Must  an  inferior  planet  always  be  in  the  same  part 
of  the  sUy  as  the  sun  ?    A  superior  planet  ? 

(See  Astronomy,  pp.  64  and  67.) 

14.  IVJty,  in  summer,  does  the  sun,  at  rising  and  at  set- 
ting, shine  on  the  north  side  of  certain  houses  ? 

Since  at  the  summer  solstice  the  sun  rises  and  sets  north  of 
the  E.  and  "W.  points,  it  will  rise  and  set  on  the  north  side  of 
a  house  which  stands  exactly  N.  and  S.  At  the  winter  solstice 
the  sun  rises  and  sets  S.  of  the  E.  and  W.  points. 

15.  Wliat  effect  does  the  volume  of  a  planet  have  upon 
the  force  of  gravity  at  its  surface  ? 

(See  Astronomy,  pp.  40,  80.) 


IN    DESCRIPTIVE    ASTRONOMY.  113 

16.  In  what  part  of  the  heavens  do  we  see  the  new 
moon  ?     The  old  moon  ?     The  crescent  moon  ? 

(See  Astronomy,  p.  127  et  seq.) 

It  is  a  very  interesting  experiment  to  notice  how  soon  after 
conjunction  we  can  observe  the  new  moon.  Observers  have  de- 
tected her  when  twenty-three  hours  old,  and  an  instance  is  on 
record  of  the  moon's  thin  crescent  being  seen  early  one  morn- 
ing before  sunrise,  and  after  sundown  the  following  day. 

17.  What  is  the  Golden  Number  in  the  almanac? 

(See  Astronomy,  p.  145.) 

18.  Why  do  we  have  more  lunar  than  solar  eclipses  ? 

(Soc  Astronomy,  p.  146.) 

Really,  solar  eclipses  occur  more  frequently  than  lunar  eclipses, 
but  the  latter  are .  of tener  seen  at  any  particular  place,  because 
they  are  visible  over  a  larger  area  of  territory  on  the  earth. 

19.  In  ivhat  direction  do  the  horns  of  the  moon  turn  ? 

(See  Astronomy,  p.  127.) 

20.  Is  the  "  tidal  wave "   a  progressive  movement  of 

the  ivater  ? 

(See  Astronomy,  note,  p.  148.) 

The  wind  raises  the  particles  of  water,  and  gravity  draws 
them  back  again.  They  thus  vibrate  up  and  down,  but  do  not 
advance.  The  forward  movement  of  the  wave  is  an  illusion. 
The  form  of  the  wave  progresses,  but  not  the  water  of  which 
it  is  composed,  any  more  than  the  thread  of  the  screw  which 
we  turn  in  our  hand,  or  the  undulations  of  a  rope  or  carpet 
which  is  shaken,  or  the  stalks  of  grain  which  bend  in  billows 
as  the  wind  sweeps  over  them.  Near  the  shore  the  oscillations 
are  shorter,  and  the  waves,  unbalanced  by  the  deep  water,  are 
forced  forward  till  the  lower  part  of  each  one  is  checked  by  the 
friction  on  the  sandy  beach,  the  front  becomes  well-nigh  ver- 
tical, and  the  upper  part  curls  over  and  falls  beyond. 

21.  Why  does  the  sun  "cross  the  line"  in  some  years 
on  March  21,  and,  in  others,  on  March  22  ? 

(See  Astronomy,  p.  99.) 

Leap-year  also  throws  the  dates  back  one  day. 


114  ANSWERS    TO    PRACTICAL     QUESTIONS 

22.  Do  we  ever  see  the  sun  where  it  really  is  ? 

(See  Astronomy,  p.  114.) 

Both  refraction  and  aberration  of  light  change  the  apparent^ 
place  of  the  sun. 

23.  "  At  Edinburgh)  Scotland,  there  are  times  when 
the  sun  rises  at  3%  o'clock  A.M.,  and  sets  at   8^  o'clock 
P.M.,  and  the  twilight  lasts  the  entire  night.9'     When  and 

why  is  this  ? 

(See  Astronomy,  p.  116.) 

The  latitude  of  Edinburgh  is  55°  57'.  Any  place  north  of 
48°  33'  will  have  twilight  at  midnight  in  midsummer ;  for  90° 
—  23°  27'  (the  sun's  declination)  —  183  (at  which  twilight  ceases) 
=  48°  33'.  The  hours  named  in  the  problem  are  the  times  for 
the  rising  and  setting  of  the  sun  at  Edinburgh  at  the  summer 
solstice. 

24.  Which  is  the  longest  day  of  the  year  ? 

(See  Astronomy,  p.  99.) 

The  summer  solstice  points  out  the  longest  day  of  the  year. 

25.  Ts  the  moon  nearer  to  us  ivlien  it  is  at  the  horizon , 
or  at  the  zenith  ? 

(See  Astronomy,  p.  124.) 

The  moon  is  nearer  to  ur,  when  it  is  at  the  zenith  than 
when  it  is  at  the  horizon. 

26.  How  many  solar  eclipses  ivould  happen  each  year 
if  the  orbits  of  the  sun  and  the  moon  ^vere  in  the  same 
plane  ? 

(See  Astronomy,  p.  138.) 

In  that  case  a  solar  eclipse  would  occur  every  new  moon. 

27.  Is  there  any  heat  in  moonlight  ? 

(See  Astronomy,  p.  125.) 

28.  Can  ive  see  the  moon  during  a  total  eclipse  ? 

(See  Astronomy,  p.  146.) 

29.  WTiicJi  of  the  planets  are  repeating  a  portion  of  the 
earth's  history  ? 

Spectrum  Analysis  renders  it  possible,  perhaps  probable, 
that  Jupiter  and  Saturn,  and,  may  be,  Uranus  and  Neptune, 


IN    DESCRIPTIVE    ASTRONOMY.  115 

have  not  yet  attained  that  degree  of  density  which  must  neces- 
sarily precede  the  formation  of  a  solid  surface.  They  are, 
therefore,  now  in  a  geologic  age  similar  to  that  in  which  the 
earth  existed  before  its  crust  had  become  solidified.  (See  Schel- 
len's  Spectrum  Analysis,  p.  337.) 

SO.  Hoiv  many  titties  does  the  moon  turn  on  her  axis 

each  year  ? 

(See  Astronomy,  p.  123.) 

The  moon  turns  on  her  axis  once  each  month. 

31.  Can  you   explain  the    different  signs  used  in  the 

almanac  ? 

(See  "Astronomical  Signs"  in  the  Dictionary.) 

32.  Shoiv  how  the  moon  is  a  prophecy  of  the  earth's 
future. 

The  moon  is  a  worn-out  globe,  and  presents  the  same  ap- 
pearance that  the  earth  will  probably  offer  ages  hence. 

33.  Does  the  sun  really  rise  and  set  ? 

(See  Astronomy,  pp.  14,  87.) 

No.  This  is  only  an  optical  illusion,  being  an  illustration  of 
our  tendency  to  transfer  motion. 

34.  Are  the  bright  portions  of  the  noon  mountains  or 
plains  ? 

The  lofty  portions,  or  mountains,  of  the  moon  reflect  the 
light  to  the  earth  most  strongly,  and  hence  appear  the  bright- 
est. The  deep  valleys,  lying  in  shadow,  look  dark. 

35.  Which  of  the  heavenly  bodies  are  self-luminous  ? 

(See  above,  Question  29 ;  also  Astronomy,  note,  p.  163.) 
Jupiter   and   Saturn  probably  emit  light,  at  least  from  the 
brighter  spots  of  their  surface.     Read  Newcomb's  Astronomy,  p. 
342. 

36.  Why  is  not  a  solar  eclipse  visible  over  the  whole 

earth  ? 

(See  Astronomy,  p.  140.) 

37.  What    is    meant    by  the    "mean  distance"   of  a 
planet  ? 

The  "mean  distance"  is  the  average  distance. 


116  ANSWERS    TO    PRACTICAL     QUESTIONS 

38.   What  keeps  the  earth  in  motion  around  the  situ  ? 

(See  Astronomy,  p.  22.) 

According  to  the  First  Law  of  Motion,  "Every  body  con- 
tinues in  its  state  of  rest  or  of  uniform  motion  in  a  straight 
line,  except  in  so  far  as  it  may  be  compelled  by  impressed 
forces  to  change  that  state." 

.7.9.  Do  we  ever  see  the  sun  after  it  sets  ? 

(Sec  Astronomy,  p.  114.) 

The  refraction  of  the  atmosphere  tends  to  raise  all  objects 
toward  the  zenith,  and,  at  the  horizon,  this  is  no  less  than  35', 
or  3'  more  than  the  mean  diameter  of  the  sun  (32'). 

40.  When  does  the  earth  move  the  most  rapidly  in  its 
orbit  ? 

(See  Astronomy,  p.  18.) 
The  earth  moves  most  rapidly  in  perihelion. 

4:1.  Have  ive  conclusive  evidence  that  any  planet  is  in- 
habited ? 

(See  Astronomy,  p.  61;  also  note,  p.  297.) 

May  it  not  be  that  the  same  lavish  hand  that  scatters  flow- 
ers and  seeds  in  such  profusion  (not  one  in  a  thousand  coming 
to  the  perfection  and  end  of  its  being),  sows  space  with  worlds, 
a  few  only  reaching  the  full  fruition  of  life  ? 

42.    When  is  tivilight  the  longest?    The  shortest?    Why? 

(See  Astronomy,  p.  116.) 

Twilight  is  usually  reckoned  to  last  until  the  sun's  depres- 
sion below  the  horizon  amounts  to  18°  ;  this,  however,  varies  ; 
in  the  tropics  a  depression  of  16°  or  17°  is  sufficient  to  put  an 
end  to  the  phenomenon,  but  in  England  a  depression  of  17°  to 
21°  is  required.  The  duration  of  twilight  differs  in  different 
latitudes  ;  it  varies  also  in  the  same  latitude  at  different  sea- 
sons of  the  year,  and  depends,  in  some  measure,  on  the  meteoro- 
logical condition  of  the  atmosphere.  Strictly  speaking,  in  the 
latitude  of  Greenwich  there  is  no  true  night  from  May  22  to 
July  21,  but  constant  twilight  from  sunset  to  sunrise.  Twilight 
reaches  its  minimum  three  weeks  before  the  vernal  equinox, 
and  three  weeks  after  the  autumnal  equinox,  when  its  duration 


IN   DESCRIPTIVE    ASTRONOMY.  117 

is  1  hr.  50  min.  At  midwinter  it  is  longer  by  about  seven- 
teen minutes ;  but  the  augmentation  is  frequently  not  percepti- 
ble, owing  to  the  greater  prevalence  of  clouds  and  haze  at 
that  season  of  the  year,  which  intercept  the  light,  and  hinder 
it  from  reaching  the  earth.  The  duration  is  least  at  the  equa- 
tor (1  hr.  12  min.),  and  increases  as  we  approach  the  poles  ; 
for  at  the  former  there  are  two  twilights  every  twenty-four 
hours,  but  at  the  latter  only  two  in  a  year,  each  lasting  about 
fifty  days.  At  the  north  pole  the  sun  is  below  the  horizon  for 
six  months,  but  from  January  29  to  the  vernal  equinox,  and 
from  the  autumnal  equinox  to  November  12,  the  sun  is  less 
than  18°  below  the  horizon ;  so  that  there  is  twilight  during 
the  whole  of  these  intervals,  and  thus  the  length  of  the  actual 
night  is  reduced  to  21  months.  The  length  of  the  day  in  these 
regions  is  about  six  months,  during  the  whole  of  which  time 
the  sun  is  constantly  above  the  horizon.  The  general  rule  is, 
that  to  the  inhabitants  of  an  oblique  sphere  the  twilight  is  longer  in 
proportion  as  the  place  is  nearer  the  elevated  pole,  and  the  sun  is 
farther  from  the  equator  on  the  side  of  the  elevated  pole. — Cham- 
bers' Astronomy. 

When  the  sun  rises  or  sets  most  obliquely  to  the  horizon, 
then  the  least  time  is  required  to  pass  through  the  necessary 
18°,  and,  of  course,  the  length  of  twilight  is  the  least.  When 
the  sun  rises  or  sets  least  obliquely,  the  most  time  is  required 
to  pass  through  18°,  and  the  length  of  twilight  is  greatest.  If 
the  sun's  path  is  perpendicular  to  the  horizon,  the  sun  will 
pass  over  the  18°  in  1  hr.  12  min.;  for  15°=  1  hr.;  and  hence 
18°  =1^  hr. 

43.  What  is  a  moon  ? 

A  moon  is  a  secondary  body,  or  satellite,  revolving  about  a 
primary  body,  or  planet. 

44.  To  a  person  in  the  south  temperate  zone,  where 
would  the  sun  be  at  noon  ? 

On  the  meridian  north  of  the  observer. 

45.  Is  it  correct  to  say  that  the  moonrevolvcs  about  the 
earth9  ivhen  ive  know  tit  at  f  according  to  the  law  of  Phys- 


118  ANSWERS    TO    PRACTICAL     QUESTIONS 

icSf  they  must  both  revolve  about  their  common  center  of 

gravity  ? 

(See  Astronomy,  note,  p.  200.) 

The  earth  is  not  stationary  as  regards  the  moon,  for  both 
it  and  our  satellite  revolve  together  about  their  common  center 
of  gravity.  Again,  it  is  not  the  earth  alone  which  revolves 
about  the  sun  in  the  elliptical  orbit,  but  this  common  center  of 
gravity.  The  sun,  also,  is  not  stationary,  but  it  and  the  planets 
revolve  about  the  common  center  of  gravity  of  the  whole 
system. 

46.  During  a  transit  of  Venus,  do  we  see  the  body  of 
the  planet  itself  on  the  face  of  the  sun  ? 

(See  Astronomy,  p.  277.) 

During  a  transit,  Venus  appears  as  "  a  perfectly  round  Nock 
spot  on  the  disk  of  the  sun."  The  planet  turns  its  unillumined 
side  toward  us,  and  is,  strictly  speaking,  invisible. 

47.  How  many  real  motions  has  the  sun  ?    How  many 
apparent  ones  ? 

It  has  two  real  motions :  one  around  its  axis,  and  one  with 
the  solar  system  around  the  Pleiades.  It  has  three  apparent 
motions  :  one  along  the  ecliptic, — its  yearly  motion  ;  one  through 
the  heavens, — its  daily  motion  ;  and  one  north  and  south. 

48.  Hoiv  many  real  motions  has  the  earth  ? 

Three.  One  on  its  axis ;  one  around  the  sun ;  and  a  third, — 
its  "wabbling  motion,"  which  causes  Precession. 

49.  Can  an  inferior  planet  have  an  elongation  of9O°  ? 

No.     Venus  recedes  only  48°  from  the  sun. 

50.  How  do  ive  know  the  intensity  of  the  sun's  lit/lit  on 
the  surface  of  any  of  the  planets  ? 

The  intensity  of  the  heat  and  light  varies  inversely  as  the 
square  of  the  distance. 

51.  IVJiy  is  the  Tropic  of  Cancer  placed  where  it  is  ? 

Because  it  is  the  farthest  place  north  where  the  sun  is  ever 
seen  directly  overhead. 


IN   DESCRIPTIVE    ASTRONOMY.  119 

52.  What  planets  would  float  in  water  ? 

According  to  Chambers'  Astronomy,  the  density  of  Saturn 
is  .68  that  of  water ;  Uranus,  .99  ;  Neptune,  .96.  According  to 
Newcomb,  Saturn's  density  is  .75. 

53.  How  must  the  moons  of  Jupiter  appear  during 
their  transit  across  the  disk  of  that  planet  ? 

The  satellites  appear  on  the  disk  of  their  primary  as  round 
luminous  spots,  preceded  or  followed  by  their  shadows,  which 
show  as  round  black  or  blackish  spots. — CHAMBERS. 

54.  "  The  shadow  of  the  satellite  precedes  the  satellite 
itself  when  Jupiter  is  passing  from  conjunction  to  oppo- 
sition)  but  follows  it  between  opposition   and    conjunc~ 
tion."    Explain. 

"When  actually  in  conjunction,  the  shadow  is  in  a  right  line 
with  the  satellite,  and  the  two  may  be  superposed. 

55.  What  facts  point  to  the  conclusion  that  Mars  may, 
perhaps,  have  passed  his  planetary  prime  ? 

The  proportion  of  land  and  water,  and  the  appearance  of 
the  seas,  all  point  to  a  conclusion  somewhat  similar  to  the  one 
stated  in  the  following  quotation  : 

"  Mars'  orbit  being  outside  the  earth's,  he  was  probably 
formed  earlier.  The  mass  of  Mars  is  not  much  more  than  \ 
the  earth's,  and  the  surface  about  |- ;  if  he  possessed  the  same 
degree  of  heat  as  the  earth,  he  would  have  only  \  the  amount 
to  radiate,  and  the  supply  would  not  last  so  long.  Though 
having  only  \  the  surface  of  the  earth,  he  would  still  cool  off  3 
times  as  rapidly  as  the  earth.  Mars  must,  therefore,  be  at 
least  three  times  as  far  on  the  way  toward  planetary  decrepi- 
tude and  death  as  our  earth." — Proctor's  Poetry  of  Astronomy. 

50.  Why  may  ^ve  conceive  that  Saturn  and  Jupiter  are 
yet  in  their  planetary  youth  ? 

(See  Astronomy,  note,  p.  163.) 

Vast  planets,  like  Saturn  and  Jupiter,  must  have  required 
for  cooling  a  far  longer  time  than  the  earth,  and  thus  the  va- 
rious stages  of  development  would  occupy  a  much  greater 


120  ANSWERS     TO    PRACTICAL     QUESTIONS 

length  of  time.     (Read  Proctor's   "  When  the  Sea  was  Young," 
in  Poetry  of  Science.) 

57  •  Show  how,  if  the  Nebular  Hypothesis  be  accepted, 
the  fashioning  of  a  planet  must  require  an  enormous 

length  of  time. 

(See  Astronomy,  p.  255.) 

The  experiments  of  Bischof  upon  basalt  show  that  the  earth 
would  require  350  millions  of  years  to  cool  down  from  2,000° 
C  to  200°  0.  This  enormous  period  would  represent  only  one 
stage  in  the  process  of  the  earth's  development.  (Read  Win- 
chell's  World  Life.) 

58.  Do  we  know  the  cause  of  gravitation  ? 

(See  Astronomy,  note,  p.  23.) 

283— 1.  In  what  constellation  is  Job's  Coffin?  The 
Letter  Y?  The  Scalene  Triangle?  The  Dipper?  The 
Kids  ?  The  Triangles  ? 

Job's  Coffin  is  in  Delphinus ;  the  Letter  Y,  in  Aquarius ; 
the  Scalene  Triangle,  in  Aries ;  the  Big  Dipper,  in  Ursa  Major  ; 
the  Kids,  in  Auriga;  and  the  Triangles,  between  Almach  and 
Arietis. 

2.  Name  some  facts  in  the  solar  system  for  ivhich  the 
Nebular  Hypothesis  fails  to  account. 

It  is  very  difficult  to  explain,  on  the  basis  of  the  Nebular 
Hypothesis,  why  the  axes  of  certain  of  the  planets  are  so 
greatly  inclined,  and,  especially,  why  the  velocity  of  the  rota- 
tion of  the  inner  moon  of  Mars  should  so  far  exceed  that  of 
Mars  itself. 

3.  Which  is  probably  hotter,  a  yellow  or  a  red  star  ? 

(See  Astronomy,  note,  p.  241.) 

When  we  heat  a  piece  of  iron,  it  first  becomes  red-hot, 
then,  as  the  temperature  rises,  other  colors  appear,  until, 
finally,  it  becomes  dazzling  white.  (See  Physics,  p.  183.) 

4.  Are  any  of  the  stars  likely  to  collide  with  each  other  ? 

Nothing  strikes  the  astronomer  more  forcibly  than  the 
thought  of  the  desolateness  of  space.  A  vast  gulf,  more  than 


IN    DESCRIPTIVE    ASTRONOMY.  121 

twenty-five  trillions  of  miles  in  width,  separates  Neptune  from 
the  nearest  fixed  star.  It  has  been  estimated  that  the  average 
distance  between  two  of  the  sixty  millions  of  fixed  stars  visible 
to  our  largest  telescopes,  is  about  nine  millions  of  millions  of 
miles.  With  this  amount  of  "elbow-room,"  a  collision  between 
any  two  such  remote  neighbors  would  be  almost  impossible. 
Yet,  Sir  Wm.  Thomson  remarks:  "It  is  as  sure  that  collisions 
must  occur  between  great  masses  moving  through  space,  unless 
guided  in  their  paths,  as  it  is  that  ships,  steered  without  intelli- 
gence, could  not  cross  and  recross  the  Atlantic  for  thousands  of 
years  with  immunity  from  collisions." 

t>.  Is  the  real  day  longer  or  shorter  than  the  apparent 
one? 

(See  Astronomy,  p.  264.) 

6.  Do  we  ever  see  the  stars  ?  . 

(See  Astronomy,  p.  203.) 

7.  What  fined  star  is  nearest  the  earth  ? 

(See  Astronomy,  pp.  204,  241.) 

8.  Hoiv  often  is  Polaris  on  the  meridian  of  a  place? 

As  Polaris  revolves  about  the  true  pole  in  a  circle,  the 
radius  of  which  is  nearly  l|-°,  it  follows  that  in  every  twenty- 
four  hours  it  is  once  on  the  meridian  below  the  pole,  and,  also, 
once  above  it.  The  diameter  of  this  circle  is  the  length  of 
Orion's  Belt,  the  stars  at  the  right  and  the  left  of  the  central 
one  representing  the  distance  the  polar  star  goes  to  the  right 
and  left  of  the  pole. 

9.  How  do  we  Jcnow  that  the  stars  are  suns  ? 

(See  Astronomy,  pp.  205,  261.) 
Spectrum  analysis  proves  this  to  be  the  fact. 

10.  Can  a  watch  keep  apparent  time? 

(See  Astronomy,  p.  265.) 

11.  How  could  a  child  be  eight  years  old  before  a  re- 
turn of  its  birthday  ? 

An  infant  born  on  Feb.  29,  1796,  did  not  have  a  birthday 
proper  until  Feb.  29,  1804,  since  the  year  1800,  not  being 


122  ANSWERS    TO    PRACTICAL     QUESTIONS 

divisible  by  400,  was  not  a  leap-year.     Many  other  such  dates 
may  be  named. 

12.  When  will  a  watch  and  a  sun-dial  agree  ? 

(See  Astronomy,  p.  265.) 

13.  What  star  will  be  the  Pole  Star  next  after  Polaris  ? 

(See  Astronomy,  p.  217.) 

14.  Why  is  the  birthday  of  Washington  celebrated  on 
Feb.  22,  ivhen  he  ivas  born  Feb.  11,  1732  (O.  8.}  ? 

(See  Astronomy,  note,  p.  312.) 

15.  Does  the  tide  have  any  effect  on  the  length  of  the 

day? 

(See  Astronomy,  notes,  pp.  89,  303.) 

16.  Will  the  jBiff  Dipper  always  look  as  it  does  now  ? 

(See  Astronomy,  note,  p.  217.) 

The  following  figure,  taken  from  Proctor's  Easy  Star  Les- 
sons, represents  the  location  of  the  seven  stars  comprising  the 
Big  Dipper,  as  they  will  be  seen  100,000  years  hence  : 


*/? 


17 •  Hoiv  many  times  docs  the  earth  turn  on  its  axis 
every  year  ? 

(See  Astronomy,  p.  264.) 

18.  Does  the  spectroscope  tell  us  any  thing  concerning 
the  constitution  of  the  moon,  or  any  of  the  planets  ? 

These  bodies  shine,  in  general,  by  reflected  light ;  therefore, 
the  light  examined  comes  from  the  sun.  By  comparing  this  re- 
flected light  with  solar  light,  the  change  produced  by  the  planet's 
atmosphere  may  be  detected.  The  lunar  spectrum  exactly 
accords  with  the  solar  spectrum.  The  spectra  of  Venus,  Mars, 
Jupiter,  and  Saturn  contain  absorption  lines  indicating  aqueous 
vapor.  Bead  Schellen's  Spectrum  Analysis,  p.  333. 

19.  When  the  United  States  bought  Alaska  from  Rus- 
sia, the  calendar  used  there  was  found  to  be  one  day  ahead 
of  our  reckoning.     Why  was  this  ? 


IN    DESCRIPTIVE    ASTRONOMY.  123 

One  going  around  the  world  westward  will  lose  a  day  in 
his  reckoning  ;  one  going  eastward  will  gain  a  day.  The  Alaska 
calendar  was  established  by  those  who  came  from  the  West  to 
this  continent,  and  their  Tuesday  corresponded  to  our  Monday. 

20.  Why  do  the  dates  of  the  solstices  and  equinoxes 
vary  a  day  in  different  years  ? 

(See  Astronomy,  p.  99.) 

Leap-year  advances  the  dates  one  day. 

21.  Why  are  not  forenoon  and  afternoon  of  the  same 
day,  as  given  in  the  almanac,  of  equal  length  ? 

(See  Astronomy,  p.  265.) 

Apparent  noon  marks  the  middle  of  the  day ;  but  mean 
noon  may  be  either  before  or  after  the  apparent  noon;  i.e., 
the  time  when  the  real  sun  is  on  the  meridian. 

22.  In  ivhat  part  of  the  heavens  (in  our  latitude)  do 
the  stars  apparently  move  from  west  to  east? 

The  northern  circumpolar  constellations  revolve  about  the 
North  Pole,  and,  during  a  part  of  their  paths,  they  apparently 
move  from  west  to  east. 

23.  What  year  was  only  nine  months  and  sioc  days 

long  ? 

(See  Astronomy,  note,  p.  312.) 

24.  What  day  ivill  be  the  last   day  of  the  nineteenth 
century  ? 

December  31,  1900. 

25.  If  one  should  watch  the  sky,  on  a  winter's  evening, 
from  6  P.M.    to  6  A.M.,  ivhat  portion   of  the    celestial 
sphere  would  he  be  able  to  see  ? 

All  that  is  ever  seen  in  his  latitude. 

26.  How  do  ive  know  that  the  moon  has  little,  if  any, 
atmosphere  ? 

Because  when  the  moon  occults  a  star,  there  is  no  refrac- 
tion of  the  star's  true  place. 


124  ANSWERS    TO    PRACTICAL    QUESTIONS 

27.  lit,  Greenland,  at  what  part  of  the  year  will  the 
midnight  sun  be  seen  due  north  ? 

At  all  places  whose  latitude  is  66°  30'  N.,  the  sun  will  be 
on  the  northern  horizon  at  midnight  of  the  summer  solstice. 
At  all  places  north  of  the  Arctic  Circle  the  sun  will  remain 
above  the  horizon,  even  at  midnight,  for  a  certain  portion  of 
the  summer,  the  number  of  days  increasing  with  the  latitude. 
Read  Ball's  Elements  of  Astronomy,  p.  142. 

28.  Can  you  give  any  other  proof  of  the  rotundity  of 
the  earth9  besides  that  named  in  the  teoct  (p.  85)  ? 

(See  Astronomy,  note,  p.  299.) 

A  sphere  is  the  only  body  that  always  presents  to  us  the 
form  of  a  circle,  no  matter  in  what  direction  we  view  it.  At 
sea,  the  circular  form  of  the  horizon  is  even  more  evident  than 
on  land. 

29.  Point  out  the  error  in  tJie  following  passage  from 
Byron's  "Darkness,"  where  the  poet,  in  describing  the 
effect  of  tJie  sun's  destruction,  says : 

"  I  had  a  dream,  .  .  . 

.  .  .  which,  was  not  all  a  dream ; 
The  bright  sun  was  extinguished,  and  the  stars 
Did  wander  darkling  in  the  external  space 
Eayless  and  pathless." 

The  fixed  stars  would  be  unaffected  by  the  extinction  of  the 
sun's  light. 

30.  Explain  the  rernarh  of  the  First  Carrier  in  Scene 
I.,  Act  II.,  King  Henry  IV. :  "An't  be  not  four  by  the  day, 
I'll  be  hanged:  Charles'  wain  is  over  the  new  chimney." 

(See  Astronomy,  note,  p.  311.) 

Since  the  two  great  stars  which  mark  the  summit  and  the 
foot  of  the  Cross  have  nearly  the  same  right  ascension,  it  fol- 
lows that  the  constellation  is  almost  perpendicular  at  the  mo- 
ment when  it  passes  the  meridian.  This  circumstance  is  known 
to  every  nation  that  lives  beyond  the  tropics  or  in  the  Southern 
Hemisphere.  It  has  been  observed  at  what  hour  of  the  night, 
in  different  seasons,  the  Cross  of  the  south  is  erect  or  inclined. 
It  is  a  time-piece  that  advances  very  regularly  near  four  min- 


AV    DESCRIPTIVE    ASTRONOMY.  125 

utes  a  day,  and  no  other  group  of  stars  exhibits  to  the  naked 
eye  an  observation  of  time  so  easily  made.  How  often  have 
we  heard  our  guides  exclaim  in  the  savannas  of  Venezuela,  or 
in  the  desert  extending  from  Lima  to  Truxillo,  "Midnight  is 
past,  the  Cross  begins  to  bend  ! "  How  often  those  words  re- 
minded us  of  that  affecting  scene,  where  Paul  and  Virginia, 
seated  near  the  sources  of  the  river  of  Lataniers,  conversed 
together  for  the  last  time,  and  where  the  old  man,  at  the  sight 
of  the  Southern  Cross,  warns  them  that  it  is  time  to  separate. 
— HUMBOLDT. 

31.  Why  does  not  the  earth  move  with  equal  velocity  in 
all  parts  of  its  orbit  ? 

Because  at  perihelion  it  is  nearer  the  sun  than  when  in 
aphelion,  and  hence  the  attraction  is  stronger. 

32.  How  many  Jovian-years  old  are  you  ? 

A  Jovian-year  equals  11.86  earth-years. 

33.  Why  is  the  sky  blue  ? 

The  blue  light  of  the  firmament  is  light  reflected  by  solid 
particles — generally  of  aqueous  vapor — in  the  air.  It  is  notice- 
able that  early  in  the  morning  and  late  at  night,  when  the 
sun's  rays  fall  obliquely  upon  the  atmosphere,  they  are  polar- 
ized by  reflection.  The  reflected  light  is  blue ;  the  transmitted 
light  of  the  sky  is  orange  or  red.  (Read  Tyndall's  Light,  p. 
152.) 

34.  At  ivhat  season  of  the  year  does  CJiristmas  occur  in 

Australia  ? 

(See  Astronomy,  Art.  vii.,  p.  98.) 

35.  Wliat  causes  the  apparent  movement  of  the  sun 
nortJi  and  south  ? 

(See  Astronomy,  p.  95.) 

It  is  caused  by  the  fact  that  the  axis  of  the  earth  is  inclined 
to  the  plane  of  the  ecliptic,  while  the  earth  is  revolving  about 
the  sun. 

36.  On  what  part  of  the  earth  is  the  twilight  tlie  long- 
est?    Tlie  shortest? 

(See  Astronomy,  p.  116 ;  Manual,  p.  116.) 


126  ANSWERS    TO    PRACTICAL     QUESTIONS 

"  Where  the  air  is  unusually  full  of  condensed  vapor,  as 
occurs  in  polar  regions,  the  twilight  is  greatly  lengthened ; 
where  the  air  is  unusually  dry,  as  occurs  in  the  tropics,  twilight 
is  said  sometimes  to  be  shortened  to  fifteen  minutes." 

37.  Name  the  causes  which  make  our  summer  longer 
than  winter. 

(See  Astronomy,  p.  102.) 

38.  Why  is  not  total  darkness  produced  when  a  dense 
cloud  passes  between  us  and  the  sun  ? 

(See  Astronomy,  p.  117.) 

39.  Why  does  the  time  of  the  tide  vary  each  day  ? 

(See  Astronomy,  p.  148.) 

40.  Why  is  an  annular  longer  than  a  total  eclipse  ? 

(See  Astronomy,  p.  140.) 

4:1.  Why  is  it  colder  in  winter  than  in  summer  ? 

(See  Astronomy,  pp.  97,  98.) 

42.  Do  the  solar  spots  affect  our  iveather  ? 

(See  Astronomy,  p.  48.) 

43.  Can  the  moon  be  eclipsed  in  the  day-time  ? 

(See  Astronomy,  p.  114.) 

44.  Why  are  the  sidereal  days  of  uniform  length  ? 

Because  of  the  almost  absolute  uniformity  of  the  earth's 
rotation. 

45.  Why  are  not  the  solar  days  of  uniform  length  ? 

(See  Astronomy,  p.  266.) 

46.  What  do  the  moon9s  phases  prove  ? 

The  moon's  phases  prove  that  she  is  spherical,  and  shines 
by  the  reflected  light  of  the  sun. 

47.  Why  do  the  sun  and  moon  appear  flattened  when 

near  the  horizon  ? 

(See  Astronomy,  p.  115.) 

48.  How  many  stars  can  we  see  with  the  naked  eye  ? 

No  one  sees  more  than  6,000,  and  few  more  than  4,000  stars. 


'IN   DESCRIPTIVE    ASTRONOMY.  127 

49.  Is  there  ever  an  annular  eclipse  of  the  moon  ? 

(See  Astronomy,  p.  146.) 

50.  "  While  the  sun  rises  and  sets  365  times,  a  star 
rises  and  sets  366  times."    Explain. 

/,  p.  264.) 


51.  How  many  moons  are  there  in  the  solar  system  ? 

Twenty  have  been  discovered. 

52.  What  causes  the  twinkling  of  the  stars  ? 

(See  Astronomy,  p.  207.) 

Some  attribute  the  twinkling  of  the  stars  to  the  inequality 
of  refraction  due  to  the  constant  changes  in  the  density  of  the 
air,  produced  by  the  constant  changes  in  the  heat. 

53.  Name  some  of  the  uses  of  the  stars. 

(See  Astronomy,  pp.  212,  285.) 

54.  Describe  the  methods  by  which  we  determine  the 
distance  of  the  sun  from  the  earth. 

(See  Astronomy,  p.  275.) 

55.  Why  do  not  the  signs  and  the  constellations  of  the 

Zodiac  agree  ? 

(See  Astronomy,  pp.  106,  211.) 

56.  Wlien  we  look  at  the  North  Star,  how  long  since  the 
light  that  enters  our  eye  has  left  that  body  ? 

(See  Astronomy,  p.  218.) 

57.  In  what   direction    does   a  comet's  tail  generally 

point  ? 

(See  Astronomy,  note,  p.  306.) 

58.  What  is  the  cause  of  shooting  stars  ? 

(See  Astronomy,  p  182.) 

59.  Why  does  the  crescent  moon  appear  larger  than 
the  dark  body  of  the  moon  ? 

(See  Astronomy,  p.  123.) 

60.  THiat  is  the  real  path  of  the  moon  ? 

(See  Astronomy,  pp.  123,  301.) 

61.  What  ^vould  be  the  result  if  the  aocis  of  the  earth 
were  parallel  to  the  plane  of  its  orbit  ? 

(Sec  Astronomy,  Article  xx.,  p.  103.) 


128  ANSWERS    TO    PRACTICAL     QUESTIONS 

62.  Do  we  see  the  same  stars  at  different  seasons  of  the 

year  ? 

(See  Astronomy,  pp.  92,  93.) 

63.  Why   do   we   not  perceive   the  earth's  motion  in 
space  ? 

Because  all  the  objects  around  us  partake  of  its  motion. 

64.  Did  the  earth  ever  shine  as  a  star  ?    Does  it  now 
shine  as  a  planet  ? 

The  earth,  doubtless,  shone  as  a  star  while  it  was  yet  a 
glowing  mass ;  now,  it  reflects  the  sun's  light,  like  the  other 
planets. 

65.  IVJiat  is  the  nebular  hypothesis  ? 

(See  Astronomy,  p.  255.) 

66.  JVJiat  is  the  cause  of  the  solar  spots  ? 

(See  Astronomy,  p.  54.) 

6*7.  Would  it  make  the  new  moon  "  drier  "  or  "  wetter  " 
if  the  moon's  path  ran  north  of,  instead  of  on,,  the  ecliptic 
at  the  time  of  new  moon  ? 

The  moon's  latitude  varies  from  5°  N.  to  5°  S.  (exactly  5° 
8'  47"  9).  If  the  new  moon  were  5°  1ST.,  this  would  increase 
the  angle  of  72^°  (note,  p.  30)  to  77£°,  and  thus  make  the  line 
joining  the  moon's  cusps  more  nearly  parallel  to  the  horizon. 
It  may  be  easily  seen  that  whenever  the  plane  of  the  lunar 
orbit  lies  so  as  to  carry  the  moon  past  conjunction  above  the 
sun,  then  the  crescent  is  more  nearly  horizontal ;  when  below, 
then  it  is  more  nearly  vertical. 

68.  Under  what  conditions  are  we  accustomed  to  trans- 
fer motion  ? 

(See  Astronomy,  pp.  85,  86.) 

69.  Wliy  do  not  the  planets  twinkle  ? 

(See  Astronomy,  note,  p.  207.) 

70.  IVliy  is  the  horizon  a  circle  ? 

(See  Manual,  p.  124,  Question  28.) 

7 !•  What  causes  are  gradually  increasing  the  length  of 

the  day  ? 

(See  Astronomy,  notes,  pp.  89,  303.) 


DESCRIPTIVE    ASTRONOMY. 


129 


year  ? 


IVliat  distance  does  the  moon  gain  in  her  orbit  each 

(See  Astronomy,  notes,  pp.  89,  302.) 


75.  State  the  general  argument  which  renders  it  prob- 
able that  other  worlds  are  inhabited. 

(See  Astronomy,  p.  63;  also,  note,  p.  297.) 

74.  Illustrate  the  uniformity  of  Nature.    What  thought 
does  this  suggest  ? 

(See  Astronomy,  p.  55;  also,  note,  p.  297.) 

So  far  as  we  can  judge,  the  laws  of  Nature,  the  properties 
of  matter,  etc.,  are  uniform  throughout  the  universe,  and  re- 
veal the  workmanship  of  one  Creator. 

75.  At  ^vhat   rate   are  we  traveling  througJi   space? 
How  is  this  determined  ? 

The  mean  orbital  velocity  of  the  earth  is  18.4  miles  per 
second.  Knowing  the  circumference  of  its  yearly  path,  the  rate 
of  motion  is  easily  calculated. 

76.  Why  does  the  length  of  a  degree  of  latitude  increase 
in  going  from  the  equator  toward  either  pole  of  the  earth  ? 

Because  the  form  of  the  earth  is  not  perfectly  spherical,  but 
is  flattened  at  the  poles  and  bulged  at  the  equator. 

LENGTH  OF  DEGREE  OF  LATITUDE. 


COUNTRY. 

LATITUDE. 

LENGTH  OF 
DEGREE. 

Sweden  

66C 
66 
58 
56 
54 
54 
52 
52 
52 
46 
44 
42 
39 
16 
12 
1 
33 
35 

20' 
19 
17 
3 
58 
8 
32 
35 
2 
52 
51 
59 
12 
8 
32 
31 
18 
43 

10"  N. 
37 
37 
55-5 
26 
13-7 
16'6 
45 
19'4 
2 
2*5 
0 
0 
21-5 
20-8 
0-4  S. 
30 
20 

Feet. 
365744 
367086 
365368 
365291 
365420 
365087 
365300 
364971 
364951 
364872 
364572 
364262 
363786 
363044 
362956 
363626 
364713 
364060 

Sweden                  

Russia  

Russia  

Prussia   .... 

Denmark  .... 

Hanover  .... 

England.  

England  

Prance  

France  

Rome.  .         ....        

America  .  .  . 

India  . 

India  .... 

Peru 

Cape  of  Good  Hope  

Cape  of  Good  Hope  

130  ANSWERS    TO    PRACTICAL     QUESTIONS 

77.  How  can  you  detect  the  yearly  motion  of  the  sun 
among  the  stars  ? 

(See  Astronomy,  first  note,  p.  94.) 

78.  Have  you  actually  traced  the  movement  of  any  one 
of  the  planets,  so  as  to  understand  its  peculiar  and  irregu- 
lar wandering  among  the  stars  ? 

Pupils  should  be  encouraged  to  watch  the  various  move- 
ments of  the  heavenly  bodies.— Read  a  thoughtful  and  sug- 
gestive article  upon  Astronomy  in  High  Schools,  in  Popular 
Science  Monthly,  Vol.  xx.,  p.  300. 

79.  Hoiv  do  you  explain  the  varied  aspect  of  the  heav- 
ens in  the  different  seasons  of  the  year  ? 

(See  Astronomy,  p.  92.) 

80.  How  does  the  spinning  of  a  top  illustrate  the  sub- 
ject of  precession? 

(See  Astronomy,  p.  109.) 

81.  Why  do  solar  eclipses  come  on  from  the  west  and 
cross  to  the  east,  while  lunar  eclipses  come  on  from  the  east 
and  cross  to  the  west  ? 

The  moon  is  moving  from  west  to  east  around  the  earth. 
In  a  solar  eclipse,  her  shadow  first  strikes  the  western  edge  of 
the  sun  ;  in  a  lunar  eclipse,  the  eastern  edge  of  the  moon  first 
strikes  the  shadow  of  the  earth. 

The  monthly  motion  of  the  moon  from  west  to  east  should 
be  carefully  distinguished  from  the  daily  motion  caused  by  the 
earth's  rotation. 

82.  Newcomb,  in  his  Astronomy,  says  that,  "  If,  when 
the  inoon  is  near  the  meridian,  an  observer  could  in  a  mo- 
ment jump  from  New  York  to  Liverpool,  keeping  his  eye 
fioced  upon  that  body,  he  could  see  her  apparently  jump  in 
the  opposite  direction  about  the  same  distance."    Explain. 

This  is  an  illustration  of  transferred  motion. 

83.  Wlien,  and  by  whom,  was  the  basis  of  the  calendar 
we  now  use  fully  established  ? 

The  Koman  calendar   had    become   involved   in   confusion, 


IN   DESCRIPTIVE    ASTRONOMY.  131 

when  Julius  Caesar,  who  possessed  no  little  astronomical  knowl- 
edge, called  to  his  assistance  a  Greek  astronomer  named  Sosig- 
enes,  and  adjusted  the  civil  year  to  the  astronomical  year. 
By  intercalating  the  extra  day  of  leap  year,  he  introduced 
what  is  known  as  the  Julian  Calendar,  which  is  still  in  use. 

The  Persian  Calendar,  invented  in  the  eleventh  century  as 
a  correction  of  the  Julian,  is  remarkable  for  its  accuracy;  it 
consists  in  making  every  fourth  year  bissextile  seven  times  in 
succession,  and  making  the  change  for  the  eighth  time  in  the 
fifth  year  instead  of  the  fourth.  This  is  equivalent  to  reckon- 
ing the  tropical  year  as  SGS^  days,  which  exceeds  the  period 
determined  by  astronomers  only  by  0.0001823  of  a  day,  or 
only  |  of  a  second,  so  that  it  would  require  a  great  number  of 
centuries  to  displace  sensibly  the  commencement  of  the  civil 
year. 

The  Gregorian  Calendar  usually  employed  is  somewhat  less 
exact,  but  it  is  more  easily  reduced  to  days,  years,  and  centu- 
ries, which  is  one  of  the  most  important  objects  of  a  calendar. 
It  consists  in  employing  a  bissextile  year  every  fourth  year, 
suppressing  three  bissextiles  in  three  centuries,  and  replacing 
one  in  the  fourth.  Thus  in  every  400  years  there  are  reckoned 
only  97  leap  years,  making  the  length  of  the  year  365^, 
which  exceeds  the  tropical  year  by  0.0002581  of  a  day,  or  very 
nearly  one  second. 

If,  following  the  analogy  of  the  Gregorian  Calendar,  our 
successors  shall  suppress  a  bissextile  every  4,000  years,  so  as  to 
make  969  instead  of  970  leap  years  in  that  interval,  the  length 
of  the  year  would  become  365¥9^  days,  or  365.2422500  days, 
instead  of  365.242219  days,  as  determined  by  observation.— 
Haughton's  Astronomy. 

84.  How  much  is  the  Russian  reckoning  of  time  be- 
hind  ours  ? 

The  Russian  reckoning  is  twelve  days  behind  us. 

85.  Is  there  any  gain  in  having  the  astronomical  and 
the  calendar  year  agree  ? 

It  is  difficult  to  show  what  practical  object  is  attained  by 
such  coincidence.  It  is  important  that  summer  and  winter, 


132  ANSWERS    TO    PRACTICAL     QUESTIONS 

seed-time  and  harvest,  shall  occur  at  the  same  time  of  the  year 
through  several  successive  generations ;  but  it  is  not  of  the 
slightest  importance  that  they  should  occur  now  at  the  same 
time  that  they  did  5,000  years  ago.— Read  Newcomb's  As- 
tronomy, p.  50. 

86.  What  religious  festival  is  fixed  each  year  by  the 
motion  of  the  moon  ? 

Easter  occurs  on  the  Sunday  after  the  first  full  moon  fol- 
lowing the  spring  equinox.— Read  article  on  Easter,  in  Apple- 
tons'  Cyclopedia. 

87.  Wliy  can  we,  at  different  times,  see  both  poles  of 
the  planet  Mars  ? 

Because  the  axis  of  the  planet  is  so  much  inclined  to  the 
plane  of  the  ecliptic. 

88.  Wliat  famous  astronomical  discovery  was  made 
on  the  first  day  of  this  century  ? 

(See  Astronomy,  p.  155.) 

89.  Do  the  stars  rise  and  set  at  the  poles  ? 

(See  Astronomy,  p.  102.) 

"At  one  of  the  poles  of  the  earth,  the  axis  of  the  earth's 
rotation  would  be  vertical,  and  pass  through  the  zenith,  and 
consequently  all  the  celestial  objects  would  appear  to  travel  in 
horizontal  circles,  parallel  to  the  horizon,  traversing  these  hori- 
zontal circles  once  in  23  hours  56  minutes  4  seconds." 

90.  Name  and  locate  the  stars  of  the  first  magnitude 
which  are  seen  in  our  sky. 

The  twenty  brightest  stars  in  the  heavens,  or  first  magni- 
tude stars,  are  as  follows:  they  are  given  in  the  order  of 
brightness. — LOCKYER. 

Sirius,  in  the  constellation       Canis  Major. 

Canopus,  "  Argo. 

Alpha,  "  Centaur. 

Arcturus,  "  Bootes. 

Rigel,  "  Orion. 

Capella,  "  Auriga. 


IN    DESCRIPTIVE    ASTRONOMY.  133 

Vega,  in  the  constellation        Lyra. 

Procyon,  "  Canis  Minor. 

Betelgeuse,  "  Orion. 

Achernar,  "  Eridanus. 

Aldebaran,  "  Taurus. 

Beta  Centauri,  "  Centaur. 

Alpha  Crucis,  "  Crux. 

Antares,  "  Scorpio. 

Altair,  "  Aquila. 

Spica,  "  Virgo. 

Fomalhaut,  "  Piscis  Australis. 

Beta  Crucis,  "  Crux. 

Pollux,  "  Gemini. 

Begulus,  "  Leo. 

91.  Name  three  bright  stars  which  lie  near  the  first 
meridian. 

a  Andromedae  ;  y  Pegasi ;  and  j3  Cassiopeiae. 

92.  What  events  ivere   transpiring  in   our  history  a 
Saturnian  century  ago  ? 

A  Saturnian-year  equals  29.45  Earth-years  ;  a  "  Saturnian 
century  ago"  was,  therefore,  2,945  years  since,  or  about  1060 
B.C.  This  was  about  the  time  of  the  rise  of  Tyre,  the  reign  of 
King  David,  etc. — Read  Barnes'  General  History,  p.  79. 

93.  What  is  the  sun's  declination  at  the  winter  solstice  ? 
At  the  autumnal  equinox  ? 

(1.)  23|°  S.     (2.)  0. 

94.  Will  the  width  of  the  terrestrial  zones  always  re- 
main exactly  as  now  ? 

(See  Astronomy,  p.  111.) 

95.  Is  it  always  noon  at  12  o'clock  ? 

(See  Manual,  p.  123,  Question  21.) 

96.  Wlien  the  sun's  declination  is  23^°  N.9  in  what  sign 
is  he  then  located,  and  what  is  his  It.  A.? 

(See  Astronomy,  p.  31.) 

This  is  the  time  of  the  summer  solstice,  and  the  sun  is  in 
Cancer,  the  fourth  sign. 


134  ANSWERS    TO    PRACTICAL     QUESTIONS 

97.  What  is  the  apparent  diameter  of  the  sun  ? 

The  mean  apparent  diameter  of  the  sun  is  32'. 

98.  How  can  a  sailor  find  Jtis  latitude  and  longitude  at 

sea? 

(See  Astronomy,  p.  280.) 

99.  How  many  miles  on  the  solar  disk  represent  a  sec- 
ond of  apparent  diameter  ? 

V  on  the  solar  disk  equals  450.3  miles. — YOUNG.  "The 
spider-line  used  in  a  large  telescope  will  cover  a  portion  of  the 
sun's  surface  \  of  a  second  in  breadth,  or  hide  a  strip  over  100 
miles  wide." 

100.  At  what  latitude  will  there  be  twilight  during  the 
entire  midsummer  night  ? 

(See  Manual,  p.  114,  Question  23.) 

"When  the  sun  crosses  the  meridian  at  midnight,  its  distance 
below  the  horizon  is  greater  than  when  the  sun  is  at  any  other 
part  of  its  diurnal  path.  If,  therefore,  the  depression  of  the 
sun  bellow  the  horizon  at  midnight  be  not  greater  than  18°,  the 
sun  will,  during  the  entire  night,  be  within  18°  of  the  horizon, 
and  hence  the  twilight  will  be  continuous. — It  will  be  noticed  in 
solving  all  the  problems  connected  with  twilight  (as,  for  ex- 
ample, Question  23,  p.  114,  and  Question  27,  p.  124),  that  the 
result  will  be  slightly  changed  if  the  exact  amount  of  the 
obliquity  of  the  ecliptic  (23°  27'  15")  be  used,  instead  of  the 
ordinary  statement,  23|°. 

ADDED   QUESTIONS  AND  ANSWERS. 

1.  Did  Tycho  Srahe  have  a  telescope  ? 

No.     Galileo  invented  the  telescope. 

2.  Suppose   one  should  watch   the  sky,  on  a  winter's 
evening,  from  6  P.M.  to  6  A.M.,  what  portion  of  the  celes- 
tial sphere  would  he  see  ? 

All  that  is  ever  seen  in  his  latitude. 

3.  How  do  we  find  tvhat  proportion  of  the  sun's  heat 
reaches  the  earth  ? 


IN   DESCRIPTIVE    ASTRONOMY.  135 

Calculate  the  surface  of  a  sphere  whose  radius  is  the  dis- 
tance of  the  earth  from  the  sun,  and  then  estimate  what  pro- 
portion of  that  area  the  earth  occupies. 

4 .  Hoiv  do  we  know  the  heat  of  the  sun's  rays  at  any 
planet  ? 

The  intensity  of  the  heat  and  light  varies  inversely  as  the 
square  of  the  distance. 

5.  Can  you  give  any  other  proof  than  that  named  in 
the  booh  of  the  rotundity  of  the  earth  ? 

Aeronauts,  when  at  a  proper  height,  can  distinctly  see  the 
curving  form  of  the  earth's  surface. 

6.  In  what  way  is  the  force  ivhich  acts  on  a  spinning- 
top  opposite  to  that  ivhich  produces  precession  ? 

Gravity,  acting  on  the  top,  tends  to  draw  C  P  (Fig.  40) 
from  the  perpendicular.  The  attraction  of  the  sun,  acting  on 
the  bulging  mass  of  the  earth's  equator,  tends  to  draw  C  P 
toward  the  perpendicular. 

7.  IVIiy  is  the  Tropic  of  Cancer  so  called  ? 

"When  named,  the  sun  was  probably  in  that  constellation  at 
the  time  of  the  summer  solstice.  Now,  owing  to  the  preces- 
sion of  the  equinoxes,  the  sun  is  in  the  constellation  G-emini, 
and  to  be  exact,  it  should  be  called  the  Tropic  of  Gemini.  It 
is  still,  however,  the  sign  Cancer,  as  before.  The  same  reason- 
ing applies  to  the  Tropic  of  Capricorn,  which  is  now  in  the 
constellation  Sagittarius. 

8.  In  Greenland,  at  what  part  of  the  year  will  the 
midnight  sun  be  seen  due  north  ? 

At  the  summer  solstice. 

9.  Wlien  is  the  moon  seen  high  in  the  eastern  sJcy  in  the 
afternoon,  long  before  the  sun  sets  ? 

During  the  second  quarter  before  it  comes  into  opposition. 

10.  WJiy  is  the  Ecliptic  so  called  ? 

Because  eclipses  always  occur  in  or  near  it. 


136  EXPLAINING    MIRRORS    AND    LENSES. 


EXPLAINING  MIRRORS  AND  LENSES. 

The  author  has  met  with  the  best  success  in  explaining  mir- 
rors and  lenses  to  his  pupils  by  using  the  following  method : 

A  Concave  Mirror. — Holding  up  before  his  eye  the  fore- 
finger of  each  hand,  he  represents  to  the  pupil  how  the  rays 
of  light  enter  his  eye  converging ;  how  he  then  sees  the  object 
on  diverging  rays :  thus  the  visual  angle  being  increased,  the 
apparent  size  of  the  object  is  correspondingly  increased.  By 
crossing  his  two  forefingers  before  his  eye  he  represents  the 
focus,  and  shows  how  diverging  rays  then  enter  the  eye ;  the 
object  is  seen  on  converging  rays,  the  visual  angle  is  decreased, 
and  the  apparent  size  of  the  object  correspondingly  decreased. 

A  Convex  Mirror. — Using  the  fingers  in  the  same  way,  he 
illustrates  how  diverging  rays  enter  the  eye,  the  object  is  seen 
on  converging  rays,  the  visual  angle  is  diminished,  and  the  ap- 
parent size  of  the  object  correspondingly  diminished.  The  rays 
of  light  are  not  brought  to  a  focus,  hence  the  second  effect  of  a 
concave  mirror  can  not  be  seen. 

The  same  illustration  can  be  used  in  explaining  lenses,  re- 
membering that  the  effect  of  a  convex  lens  is  like  that  of  a 
concave  mirror,  and  of  a  concave  lens  that  of  a  convex  mirror. 

At  the  close  of  the  explanation  and  illustration  with  the 
fingers,  the  following  formula  is  put  on  the  blackboard,  and  the 
pupil  applies  it  to  each  class  of  mirrors  and  lenses : 

CONVERGING  (diverging)  RAYS  ENTER  THE  EYE,  THE  OBJECT  is 

SEEN  ON    DIVERGING  (converging)    RAYS  ;    HENCE    THE  VISUAL  ANGLE 

is  INCREASED  (decreased),    AND   THE   IMAGE   is    LARGER   (smaller) 

THAN  LIFE. 


ASTRONOMY  WITH  AN  OPERA-GLASS. 

In  schools  where  there  is  no  telescope,  teachers  may  find 
valuable  suggestions  for  class  observations  in  the  articles  en- 
titled "Astronomy  with  an  Opera-Glass,"  by  Garrett  P.  Serviss, 
in  the  Popular  Science  Monthly,  April,  June,  August,  and  No- 
vember, 1887,  and  February,  1888. 


TABLE    OF    THE    MINOR    PLANETS. 


137 


TABLE   OF  THE   MINOR   PLANETS,* 

including  alt  that  have  been  discovered  to  date  (Oct.,  1887). 


ISO. 

NAME. 

DATE   OF  DISCOVERY. 

DISCOVEKEK. 

1 

Ceres 

1801,    January         1 

Piazzi. 

2 

Pallas 

1802,    March          28 

Olbers. 

3 

1804     Sept                 1 

Harding. 

4 

Vesta.          

3  807,    March          20 

Olbers. 

5 

1845     Dec                  8 

Hencke. 

g 

Hebe 

1847     July                1 

Hencke. 

7 

Iris  .                         ... 

1847,    August         13 

Hind. 

8 
9 
10 

Mora  
Metis  
Hygieia  

1847,    October        18 
1848,    April            25 
1849,    April             12 

Hind. 
Graham. 
Gasparis. 

11 
12 

Parthenopo  

1850,    May              11 
1850     Sept               13 

Luther. 
Hind 

13 
14 

Egeria  
Irene          

1850,    Nov.                2 
1851     May              19 

Gasparis. 
Hind 

15 

Eunomia  . 

1851     July              29 

Gasparis. 

16 

Psyche 

1852     March          17 

Gasparis. 

17 

Thetis 

1852     April            17 

Ijuther. 

18 

Melpomene  

1852,    Juno              24 

Hind. 

19 

Fortuna 

1852     August         22 

Hind. 

20 

Massalia 

1852     Sept              19 

Gasparis. 

21 

Lutetia  

1852,    Nov.              15 

Goldschmidt. 

°2 

Calliope 

1852     Nov.              16 

Hind. 

23 

Thalia  

1852,    Dec.              15 

Hind. 

24 

Themis  

1853,    April               5 

Gasparis. 

25 

Phocsea 

1853,    April               7 

Chacornac. 

26 

27 

Proserpina  

Euterpe 

1853,    May                5 
1853     Nov.                8 

Luther. 
Hind. 

28 
on 

Bellona  

1854,    March            1 
1854     March            1 

Luther. 
Marth 

30 

Urania. 

1854     July              22 

Hind. 

31 

Euphrosyne  

1854,    Sept.               1 

Ferguson. 

32 

Pomona  . 

1854     October        26 

Goldschmidt. 

33 
34 

Polyhymnia  
Circe.                

1854,    October        28 
1855,    April               6 

Chacornac. 
Chacornac. 

35 

Leucothea    

1855,    April            19 

Luther. 

36 

-A-talanta  . 

1855,    October          5 

Goldschmidt. 

37 

Fides 

1855,    October          5 

Luther. 

38 

Leda 

1856,    January      12 

Chacornac. 

39 

Leetitia 

1856,    February       8 

Chacornac. 

*  The  numerical  order  is  that  adopted  by  the  authority  of  the  Berlin 
Ephemeria. 


138 


TABLE  OF  THE  MINOR  PLANETS. 


NO. 

NAME. 

DATE   OF  DISCOVERY. 

DISCOVERER. 

40 

Harmonia  .  . 

1856     March          31 

41 

Daphne  

1856     May              22 

42 

Isis  

1856     May              23 

43 

Ariadne  

1857     April            15 

44 
45 

Nysa  
Eugenia 

1857,    May              27 
1857     June             W 

Q-oldschmidt. 

46 

Hestia. 

1857     August        16 

47 

Aglaia. 

1857     Sept              15 

48 

Doris. 

1857     Sept               19 

frol  c\  ^rOi  mi  c\t 

49 

Pales 

1857     Sept               19 

fro!  rl  <^rT"i  m  i  rJ  t 

50 

Virginia. 

1857     October          4 

51 

Nemausa  .. 

1858     January       2° 

52 

Europa  . 

1858     February       4 

Q-oldschniidt 

53 

Calypso 

1858     April               4 

54 

Alexandra  

1858     Sept               10 

Q-oldschmidt 

55 

56 

Pandora  
Melete* 

1858,    Sept.             10 
1857     Sept                 9 

Searle. 

57 

Mnemosyne  . 

1859     Sept              2° 

58 

Concordia 

1860     March          °4 

59 

Elpis 

1860     Sept              1° 

60 

Echo.  . 

1860     Sept               15 

61 

Danae. 

1860     Sept                 9 

G/oldschmidt 

62 

Erato  . 

1860     Sept              14 

63 

Ausonia  .. 

1861      Feb               10 

Gasparis 

64 

Angelina 

1861     March            4 

Tempel 

65 

Cybele  .    .  . 

1861     March             G 

Tempel 

66 

Maia  .. 

1861      April               9 

Tuttle 

67 

Asia.    .                   .  . 

1801      April            17 

Pogson 

68 

Leto  . 

1861     April            29 

Luther 

69 

1861     April            29 

Schiaparelli 

70 

Panopea  ..            . 

1861     May                5 

G-oldschmidt 

71 

Niobe       

1861     August         13 

Luther. 

72 

Eeronia  . 

1861     May              29 

Peters  &  Safford. 

73 

Clytie 

1862     April               7 

Tuttle. 

74 

Galatea  

1862,    August         29 

Tempel. 

75 

Eurydice 

1862      Sept               22 

Peters 

76 

Freia     .  . 

1862     October        21 

d'  Arrest. 

77 

Frisrera 

1862     Nov               12 

Peters. 

78 

Diana              ..... 

1863     March          15 

Luther. 

79 

Eurynome 

1863     Sept              14 

"Watson. 

80 

Sappho 

1864     May                2 

Pogson. 

81 

Terpsichore 

1864     Sept              30 

Tempel. 

82 

Alcmene  .  . 

1864     Nov               27 

Luther. 

*  Goldschmidt  at  first  believed  it  to  be  Daphne  (41),  but  Schubert  find- 
ing its  period  different,  called  it  Pseudo-Daphne.  It  was  not  seen  from  1857 
to  1861,  when  Luther  rediscovered  it,  and  named  it  Melete. 


TABLE    OF    THE    MINOR    PLANETS. 


139 


NO. 

NAME. 

DATE  OF  DISCOVERY. 

DISOOVEEEK. 

83 

Beatrix  

1865,    April            26 

Grasparis 

84 
85 

Clio  
lo 

1865,    August         26 
1865     Sept               19 

Luther. 
Peters 

86 

1866,    January         4 

Tietjen 

87 

Sylvia 

1866     May              16 

88 

Thisbe 

1866     June              15 

Peters 

89 

1866     August           6 

Stephan 

90 

Antiope  

1866,    October        11 

Luther. 

91 

JEgina  

1866,    Nov.                4 

Stephan. 

92 

Undina  

1867,    July                7 

Peters. 

93 

Minerva  

1867,    August         24 

Watson. 

94 

Aurora  

1867,    Sept.               6 

Watson. 

95 

Arethusa  

1867,    Nov.              23 

Luther. 

96 

^?Egle 

1  868,    February     17 

Coggia  . 

97 
98 

Clotho  
lanthe  

1868,    February     17 
1868,    April            18 

Tempel. 
Peters. 

99 

Dike  

1868,    May              28 

Borelly 

100 

Hecate  .. 

1868,    July              11 

Watson. 

101 

Helena 

1868,    August         15 

"Watson. 

102 

Miriam 

1868,    August         22 

Peters. 

103 

Hera  

1868,    Sept.               7 

Watson. 

104 

Clymene  . 

1868,    Sept.              13 

Watson. 

105 

Artemis  

1868,    Sept.             16 

Watson. 

106 

Dione  .  . 

1868,    October        10 

Watson. 

107 

Camilla  

1868,    Nov.              17 

Pogson  . 

108 

1869,    April               2 

Luther. 

109 

Felicitas  

1869,    October          9 

Peters. 

110 

Lydia  

1870,    April             19 

Borelly. 

111 

Ate 

1870,    August         14 

Peters. 

112 

Iphigenia 

1870,    Sept.             19 

Peters. 

113 

Amalthea. 

1871,    March          12 

Luther. 

114 

Cassandra  ... 

1871,    July              23 

Peters. 

115 

Thyra                   

1871,    August           6 

Watson. 

116 

Sirona. 

1871,    Sept.                8 

Peters. 

117 

Lomia. 

1871,    Sept              13 

Borelly. 

118 

Peitho  . 

1872,    March          15 

Luther. 

119 

Althsea  

1872,    April              S 

Watson. 

120 

Lachesis  

1872,    April             10 

Borelly. 

121 

Hermione 

1872     May              12 

Watson 

122 

Gerda     . 

1872     July              31 

Peters 

123 

Brunhilda  . 

1872     July              31 

Peters. 

124 

Alceste 

1872     August         23 

Peters. 

125 

Liberatrix  . 

1872     Sept               11 

Prosper  Henry. 

126 

Velleda          

1872     Nov.                5 

Paul  Henry. 

127 

Johanna  . 

1872     Nov.                5 

Prosper  Henry. 

128 

Nemesis.       

1872     Nov               25 

Watson. 

129 

Antigone.. 

1873     February       5 

Peters. 

130 

Electra,...              .  . 

1873,    February     17 

Peters. 

140 


TABLE    OF    THE    MINOR    PLANETS. 


NO. 

NAME. 

DATE   OF  DISCOVERY. 

DISCOVERER. 

131 

"Vala  .  .  . 

1873     May              26 

Peters. 

132 

.^Ethra 

1873     June             13 

"Watson. 

133 

Gyrene 

1873     August         16 

"Watson. 

134 

Sophrosyne  

1873,    Sept.             27 

Liuther. 

135 

Hertha      .  . 

1874     Feb               18 

Peters. 

130 

Austria. 

1874     March          18 

Palisa. 

137 

Melibcea 

1874     April            21 

Palisa. 

138 

Tolosa  . 

1874     May              19 

Perrotin. 

139 

Juewa  

1874     October        10 

Watson. 

140 

Siwa 

1874     October       13 

Palisa. 

141 

Lumen 

1875     January      13 

Paul  Henry. 

142 

Polana. 

1875,    January      28 

Palisa. 

143 

Adria  . 

1875,    Feb.               23 

Palisa. 

144 

"Vibilia  .    . 

1875,    June               3 

Peters. 

145 

Adeona  ....        

1875,    June               3 

Peters. 

146 

Lucina  ... 

1875,    Juno                0 

Borelly. 

147 

Protogeneia              .... 

1875,    July              11 

Schulhof. 

148 

Gallia  

1875,    August           7 

Prosper  Henry. 

149 

Medusa  

1875,    Sept.             21 

Perrotin. 

150 

Nuwa  

1875,    October        18 

"Watson. 

151 
152 

Abundantia  
Atala  

1875,    Nov.               1 
1875,    Nov.                2 

Palisa. 
Paul  Henry. 

153 

Hilda 

1875     Nov                  2 

Palisa 

154 

Bertha 

1875     Nov                  A 

Prosper  Henry 

155 
156 
157 

Scylla  
Xantippo  
Dejanira  

1875,    Nov.                0 
1875,    Nov.              22 
1875,    Dec.                1 

Palisa. 
Palisa. 
Borelly. 

158 

1876     January         4 

Knorre. 

159 
160 

Emilia  
"Una   

1876,    January      26 
1870,    February     20 

Paul  Henry. 
Peters. 

161 

1876     April            18 

"Watson 

162 

Laurentia  

187G,    April            21 

Prosper  Henry. 

163 

1876,    April            26 

Perrotin. 

164 

Eva 

1876     July              12 

Paul  Henry. 

165 

Hioreley 

1876,    August           0 

Peters. 

166 

Uhodopo 

1876,    August         15 

Peters. 

167 

Urda        

1876     August        28 

Peters. 

168 

Sibylla 

1876,    Sept.             28 

Watson. 

169 

Zelia       

1870,    Sept.             28 

Prosper  Henry. 

170 

1877     January       10 

Perrotin. 

171 

Ophelia  

1877,    January      13 

Borelly. 

172 
173 

Bancis  
Ino  

1877,    February       5 
1877,    August           2 

Borelly. 
Borelly. 

174 
175 
176 

Phaedra  
Andromache  
Idunna  

1877,     Sept.               3 
1877,    October          1 
1877,    October       14 

"Watson. 
Watson. 
Peters. 

177 
178 

Irma  
Belisana 

1877,    Nov.                5 
1877     Nov                 6 

Prosper  Henry. 
Palisa. 

179 

Clytemnestra  

1877,    Nov.              12 

Watson. 

TABLE    OF    THE    MINOR    PLANETS. 


141 


NO. 

HAME. 

DATE  OF  DISCOVERT. 

DISCOVERER. 

180 

1878,    January      29 

Perrotin 

181 

Eucharis  

1878,    February      2 

Cottenot 

182 

Elsa 

1878     February       7 

Palisa 

183 

Istria    

1878,    February       8 

Palisa 

184 

Deiopeia 

1878     February     28 

Palisa 

185 

Eunike 

1878     March            1 

Peters 

186 

Celuta  

1878,     April              6 

Prosper  Henry 

187 
188 

Lamberta  
Menippe. 

1878,    April             11 
1878     June             18 

Coggia. 
Peters 

189 

Ph.th.ia 

1878     Sept                 9 

Peters. 

190 

Ismene  

1878     Sept              22 

Peters 

191 

Kolga  

1878      Sept              30 

Peters 

192 
193 
194 

Nansicaa  
Ambrosia  
Procne  

1879,    February     17 
1879,    February     28 
1879     March          21 

Palisa. 
Coggia. 
Peters 

195 

Eurycleia.  ... 

1879      April            22 

Palisa 

196 

Philomela. 

1879     May              17 

Peters 

197 

Arete... 

1879     May              21 

Palisa 

198 

-A_mpella 

1879     June              13 

Borelly 

199 

Byblis  

1879     July                9 

Peters 

200 

Dynamene 

1879     July              27 

Peters 

201 

1879     August           7 

Palisa 

202 
203 

Chryseis  
Pompeia  

1879,    Sept.             11 
1879,    Sept.             25 

Peters. 
Peters 

204 
205 
206 

Callisto  
Martha  
Hersilia 

1879,    October          8 
1879,    October        13 
1879     October        13 

Palisa. 
Palisa. 
Peters 

207 

Hedda 

1879     October        17 

Palisa 

208 

Lacrymosa  . 

1879     October        21 

Palisa 

209 

Dido 

1879     October        22 

Peters 

210 

Isabella 

1879,    Nov               12 

Palisa 

211 

Isolda  

1879,    Dec               10 

Palisa 

212 

Medea.... 

1880     February       G 

Palisa 

213 

Ldlisea  

1880     February     16 

Peters 

214 

Aschera  

1880     March            1 

Palisa 

215 

CEnone  

1880     April              7 

216 
217 
218 
219 

Cleopatra  ... 
Eudora  
Bianca  
Thusnelda  

1880,    April             10 
1880,    August         30 
1880,    Sept.                4 
1880,    Sept.              30 

Palisa. 
Coggia. 
Palisa. 
Palisa 

220 

Stephania 

1881     May              20 

Palisa 

221 

Eos 

188^     January       18 

Palisa. 

222 
223 

Lucia  
Uosa  

1882,    February       9 
1882,    March            9 

Palisa. 
Palisa. 

224 

Oceana  

1882     March          30 

Palisa. 

225 

Henrietta  

1882,    April             19 

Palisa. 

226 

"Weringia. 

1882     July             19 

Palisa. 

227 
228 

Philosophia  
Agathe  .  .  . 

1882*,    August        12 
1882,    August        19 

Paul  Henry. 
Palisa. 

142 


TABLE  OF  THE  MINOR  PLANETS. 


NO. 

NAME. 

DATE  OF  DISCOVERY. 

DISCOVEBEB. 

229 

Adelinda  . 

1882     August        22 

Palisa 

230 

Athamantis.  . 

1882     Sept                 3 

De  Ball 

231 

"Vindobona  

1882     Sept              10 

Palisa 

232 

Russia  

1883     January       31 

Palisa 

233 

Asterope  

1883     May              11 

Borelly 

234 

Barbara  

1883     August        13 

Peters. 

235 

Caroline  

1883     Nov               29 

Palisa. 

236 

Honoria  

1884     April            26 

Palisa. 

237 

Coelestina  . 

1884     June             27 

Palisa 

238 

1884     July                1 

Knorre 

239 

Adrastea  

1884     August        18 

Palisa. 

240 

"Vanadis  

1884     August         27 

Borelly. 

241 

G/ermania    

1884     Sept              12 

Luther. 

242 

Kriemhild.  .  .. 

1884     Sept              2° 

Palisa 

040 

Ida 

1884     Sept              20 

Palisa 

244 

Sita 

1884     October        14 

Palisa. 

245 

Vera 

1885     February      G 

Poison 

246 

Asporina  ....        .... 

1885     March            0 

Borelly 

247 

Eukrate  .  .  . 

1885     March          14 

Luther 

248 

Tjiii  i  iciji     

1885     June               5 

Palisa 

249 

Use      

1885     August        17 

Peters 

250 

Bettina  

1885     Sept                 3 

Palisa 

251 

Sophia  

1885     October          4 

Palisa 

Of>Q 

1885     October        27 

253 

OCA 

Mathilda  

1885,    Nov.              12 
1886     March          31 

Palisa. 
Palisa 

255 

Oppavia    

1886     March          31 

Palisa. 

0-f» 

1886     April               3 

Palisa 

257 

Silesia       

1886     April               5 

Palisa. 

258 

Tyche   

1886     May                4 

Luther. 

259 

Altheia  

1886     June             28 

Peters. 

260 

Huberta  

1886     October          3 

Palisa. 

261 

1886     October        31 

Peters. 

262 

Valda 

1886     Nov                 3 

Palisa. 

263 

Dresda                   •  •  . 

1886     Nov.                3 

Palisa. 

264 

Libussa 

1886,    Dec.               17 

Peters. 

265 

Anna    .        

1887,    February     25 

Palisa. 

266 

Aline 

1887,    May              17 

Palisa. 

267 

Tirza        .     .        

1887,    May              27 

Charlois. 

268 

1887,    June               9 

Borelly. 

269 

1887,    Sept.             21 

Palisa. 

270 

1887,    October          8 

Peters. 

271 

1887,    October        16 

Knorre. 

Prom  this  Table,  it  will  be  observed  that,  next  to  Palisa,  of  Vienna, 
Austria,  the  one  investigator  who  has  discovered  the  largest  number  of 
asteroids  is  our  own  Dr.  Peters,  of  Clinton,  N.  Y.  It  is  probable  that  all 
the  larger  asteroids  have  now  been  identified. 


ANSWERS 


TO    THE 

QUESTIONS 

IN    THE 

HYGIENIC    PHYSIOLOGY. 

23 — !•  Why  does  not  a  fall  hurt  a  child  as  much  as  it 
does  a  grown  person  ? 

The  bones  of  a  child  are  largely  cartilaginous,  and  so  do  not 
transmit  a  shock,  or  readily  yield  to  a  blow.  They  are  also  well 
padded  with  fat. 

2.  Should   a   young  child  ever  be  urged  to  stand  or 
walk? 

No ;  bow-legs  are  often  caused  by  the  premature  use  of  the 
lower  limbs  in  standing  or  walking.  Nature  is  the  best  guide 
in  such  matters. 

3.  What  is  meant  by  "  breaking  one's  neck  "  ? 

The  dislocation  of  the  vertebrae  and  consequent  injury  of 
the  spinal  cord. 

4.  Should  chairs  or  benches  have  straight  backs  ? 

The  backs  should  conform  to  the  natural  shape  of  the  spine. 
This  tends  to  prevent  curvatures  and  other  distortions  of  the 
vertebral  column. 

5.  Should  a  child's  feet  be  allowed  to  dangle  from  a 
high  seat  ? 

The  position  is  as  unnatural  and  painful  for  a  child  as  for  a 
grown  person. 

6.  Why  can  ^ve  tett  whether  a  fowl  is  young  by  pressing 
on  the  point  of  the  breast-bone  ? 


144  ANSWERS    TO    PRACTICAL     QUESTIONS 

Because  that  part  of  the  breast-bone  is  not  ossified  in  a 
young  fowl. 

7.  What  is  the  use  of  the  marrow  in  the  bones  ? 

It  contains  the  blood-vessels  carrying  material  for  the  growth 
of  the  bone,  and  also  diffuses  any  shock  which  the  bone  may 
receive. 

8.  Why  is  the  shoulder  so  often  put  out  of  joint  ? 

Because  of  the  shallowness  of  the  socket  in  the  scapula. 
f>.  Hoiv  can  you  tie  a  knot  in  a  bone  ? 

By  removing  the  mineral  matter,  and  thus  softening  a  rib- 
bone,  a  knot  can  be  easily  tied  in  it. 

10.  Why  are  high,  pillows  injurious  ? 

They  elevate  the  head,  and  so  give  an  unnatural  position  to 
the  spine.  For  the  pads  between  the  vertebrae  to  assume  their 
proper  shape  during  the  night  they  should  be  relieved  of  all 
pressure. 

11.  Is  a  stooping  posture  a  healthy  position  ? 

No.  Such  a  posture,  made  habitual,  contracts  the  chest, 
changes  the  outline  of  the  spine,  and  diminishes  the  vitality 
of  the  system. 

12.  Ought  a  boot  to  have  a  heel-piece  ? 

A  low  and  broad  heel-piece  probably  aids  in  walking ;  a 
narrow  or  high  one  weakens  and  enlarges  the  ankle,  produces 
bunions,  corns,  etc.,  by  throwing  the  weight  forward  upon  the 
toes,  and  makes  the  gait  exceedingly  ungraceful. 

13.  Why  should  one  always  sit  and  walk  erect  ? 

Because  then  all  the  organs  are  in  their  natural  position. 
An  erect  carriage  is  as  conducive  to  health  as  to  beauty. 

14.  Why  does  a  young  child  creep  rather  than  walk  ? 

(See  Physiology,  p.  50.) 

Its  bones  not  yet  being  fully  ossified,  nature  teaches  it  not 
to  bear  its  weight  upon  them.  Besides,  it  has  not  yet  learned 
the  difficult  art  of  balancing  itself. 


IN    HYGIENIC    PHYSIOLOGY.  145 

15.  What  is  the  natural  direction  of  the  big  toe  ? 

The  natural  direction  of  the  big  toe  is  in  a  line  with  the 
long  axis  of  the  foot,  but  the  conventional  boot,  which  insists 
upon  an  even-sided  symmetry,  and  often  upon  a  narrow  tip, 
tends  to  crowd  the  extremity  of  this  toe  toward  the  middle  line 
of  the  sole.  If  well-developed  feet  are  placed  side  by  side  and 
heel  to  heel,  the  two  great  toes  will  be  found  to  be  parallel  to 
each  other,  and  to  touch  each  other  almost  to  their  very  ends. 
If  the  same  feet,  clad  in  the  shoes  of  the  period,  are  placed  in 
the  same  position,  it  will  be  found  that,  while  the  heels  are  in 
contact,  the  tips  of  the  two  great  toes  will  be  considerably 
separated. 

16.  IVTiat  is  the   difference  between  a  sprain  and   a 
fracture  ?    A  dislocation  ? 

In  a  sprain,  the  ligaments  which  bind  the  bones  of  a  joint 
are  strained,  twisted,  or  torn  from  their  attachments ;  in  a 
fracture,  the  bone  itself  is  broken ;  in  a  dislocation,  the  bone  is 
displaced  from  its  socket. 

17.  Does  the   general  health   of  the  system  affect  the 
strength  of  the  bones  ? 

Certainly.     Impoverished  blood  will  not  make  healthy  bone. 

46 — 1.  IVliat  class  of  lever  is  the  foot  ivhen  ive  lift  a 
iveiglit  on  the  toes  ? 

The  third  class.  The  ankle-joint  is  the  fulcrum,  the  weight 
is  at  the  toes,  and  the  power  is  in  front  of  the  ankle,  where 
the  muscle  which  lifts  the  toes  (the  extensor  digitorium)  is  at- 
tached to  the  foot. 

2.  Explain  the  movement  of  the  body  baclwvard  and 
forward,  ^vhen  resting  upon  the  tfiigh-botie  as  a  ful- 
crum. 

The  weight  is  at  the  center  of  gravity  of  the  head  and 
trunk,  high  above  the  hip-joints,  where  the  fulcrum  is  situated. 
The  flexor  muscles  of  the  thigh  are  the  power,  and  act  close  to 
the  fulcrum.  The  weight  is  sometimes  directly  over  the  ful- 
crum, and  may  be  on  any  side  of  it.  This  seems  to  the  author 


146  ANSWESS    TO    PRACTICAL     QUESTIONS 

to  be  an  example  of  the  first  or  second  class  of  lever.    Huxley 
gives  it  as  an  illustration  of  the  third  class. 

3.  What  class  of  lever  do  ive  use  wJien  we  lift  the  foot 
while  sitting  down  ? 

The  third  class.  The  fulcrum  is  the  knee-joint ;  the  weight 
is  at  the  center  of  gravity  of  the  foot  and  leg,  and  the  power 
is  applied  by  the  ligament  which  passes  over  the  patella. 

4.  Explain  the  swing  of  the  arm  from  the  shoulder. 

(See  Physiology,  p.  34  ) 

The  third  class.  The  fulcrum  is  the  shoulder- joint ;  the 
weight  is  at  the  center  of  gravity  of  the  arm  and  hand,  and 
the  power  is  applied  by  the  biceps  or  triceps  muscle  at  its  at- 
tachment near  the  elbow. 

5.  What  class  of  lever  is  used  in  betiding  our  fingers  ? 

The  fulcrum  is  at  the  junction  of  the  finger  with  the  palm ; 
the  weight  is  at  the  center  of  gravity  of  the  finger,  and  may 
play  about  the  fulcrum  as  stated  in  second  question.  It  is  the 
third  class  of  lever,  especially  when  force  is  exerted  at  the  ex- 
tremity of  the  fingers. 

6.  What  class  of  lever  is  our  foot  when  we  tap  the 
ground  with  our  toes  ? 

(See  Physiology,  Fig.  14,  Tc.) 

The  first  class.  The  weight  is  at  the  toe  when  the  force  is 
exerted ;  the  fulcrum  is  at  the  ankle ;  and  the  power  is  applied 
by  the  gastrocnemius  muscle  at  its  attachment  to  the  heel. 

7.  Wliat  class  of  lever  do  we  use  when  we  raise  our- 
selves from  a  stooping  position  ? 

The  third  class.  See  second  question.  If  we  are  attempt- 
ing to  lift  a  heavy  burden,  the  bones  act  on  the  principle  of 
the  toggle-joint.  "When  one  stoops  to  take  a  heavy  weight 
upon  his  back  or  shoulder,  he  puts  both  the  knee  and  the  hip- 
joints  into  the  condition  that  the  toggle-joint  is  when  it  is  bent; 
and  then,  as  he  straightens  up,  the  weight  is  raised  by  an  ac- 
tion of  the  joints  precisely  similar  to  that  of  the  toggle-joint  in 
machinery.  In  the  case  of  the  knee,  the  straightening  of  the 


IN   HYGIENIC    PHYSIOLOGY.  147 

joints  is  done  by  the  muscles  on  the  front  part  of  the  thigh, 
that  draw  up  the  knee-pan  with  the  tendon  attached  to  it. 
This  is  using  the  principle  of  the  toggle-joint  in  pressing  up- 
ward. It  is  also  sometimes  used  in  pressing  downward.  In 
crushing  any  thing  with  the  heel,  we  give  great  force  to  the 
blow  on  the  principle  of  the  toggle-joint,  by  flexing  the  knee 
and  straightening  the  limb  as  we  bring  down  the  heel  upon  the 
thing  to  be  crushed.  In  pushing  any  thing  before  us,  we  bend 
the  elbow  as  preparatory  to  the  act,  and  then  thrust  the  arm 
out  straight,  thus  exemplifying  the  toggle-joint.  The  horse 
gives  great  force  to  his  kick  in  the  same  way.  The  great 
power  exerted  by  beasts  of  draught  and  burden  is  to  be  re- 
ferred very  much  to  the  principle  of  the  toggle-joint.  When  a 
horse  is  to  draw  a  heavy  load,  he  bends  all  his  limbs,  especially 
the  hinder  ones,  and  then  as  he  straightens  them,  he  starts  the 
load.  In  this  case  the  ground  is  the  fixed  block  of  the  mechan- 
ism, the  body  of  the  horse  to  which  the  load  is  attached  is  the 
movable  one,  and  his  limbs  are  so  many  toggle-joints.  By  this 
application  of  the  principle,  we  see  draught  horses  move  very 
heavy  loads." — HOOKER'S  Physiology.  "So  (admitting  fable  to  be 
fact),  when  the  farmer,  in  answer  to  his  petition  for  assistance, 
was  commanded  by  Hercules  to  exert  himself  to  raise  his  wagon 
from  the  pit,  he  placed  his  shoulder  against  the  wheel,  and 
drawing  his  body  up  into  a  crouching  attitude,  whereby  all  his 
joints  are  flexed,  and  making  his  feet  the  fixed  points,  by  a 
powerful  muscular  effort,  he  straightened  the  toggle-joints  of 
his  limbs,  and  the  wheel  was  raised  from  its  bed  of  miry  clay. 
His  horses  at  the  same  moment  extending  their  joints,  the 
heavily  laden  wagon  was  carried  beyond  the  reach  of  further 
detention. "— G-BISCOM. 

8.  What  class  of  lever  is  the  foot  when  we  walk  ? 

In  the  first  stage  it  is  clearly  the  second  class.  (See  Physi- 
ology, Fig.  18.)  The  fulcrum  is  the  ground  on  which  the  toes 
rest ;  the  power  is  applied  by  the  gastrocnemius  muscle  (see 
Fig.  14,  ft)  to  the  heel ;  the  resistance  is  so  much  of  the  weight 
of  the  body  as  is  borne  by  the  ankle-joint  of  the  foot,  which  of 
course  lies  between  the  heel  and  the  toes. 


148  ANSWERS    TO    PRACTICAL     QUESTIONS 

9.  Why  can  we  raise  a  heavier  iveight  with  our  hand 
when  liftinrj  with  the  elbow  than  from  the  shoulder? 

Because  we  bring  the  fulcrum  .nearer  the  power.  In  the 
former  case  it  is  at  the  elbow ;  in  the  latter,  at  the  shoulder. 

10.  Wliat  class  of  lever  do  ^ve  employ  when  ive  are  hop- 
ping, the  thigh-bone  being  bent  up  toward  the  body  and 
not  used  ? 

In  this  case  the  fulcrum  is  at  the  hip-joint.  The  power 
(which  may  be  assumed  to  be  furnished  by  the  rectus  muscle* 
of  the  front  of  the  thigh)  acts  upon  the  knee-cap ;  and  the  po- 
sition of  the  weight  is  represented  by  that  of  the  center  of 
gravity  of  the  thigh  and  leg,  which  will  lie  somewhere  between 
the  end  of  the  knee  and  the  hip. — HUXLEY. 

11.  Describe    the  motions   of  the  bones  when  we  are 
using  a  gimlet. 

The  radius  rolls  on  the  ulna  at  the  elbow,  while  the  ulna 
rolls  on  the  radius  at  the  wrist.  The  two  combined  produce  a 
free,  rotary  motion. 

12.  Wliy  do  we  tire  when  we  stand  erect  ? 

(See  Physiology,  p.  37.) 

Because  so  large  a  number  of  muscles  must  be  in  constant 
action  to  maintain  this  position. 

13.  Why  does  it  rest  us  to  change  our  work  ? 

"We  thereby  bring  into  use  a  new  set  of  muscles. 

14.  !V7iy  and  when  is  dancing  a  beneficial  exercise? 

When  dancing  is  performed  out-of-doors,  or  in  a  well-ven- 
tilated room,  and  at  proper  hours,  it  is  doubtless  a  beneficial 
exercise,  since  it  employs  the  muscles  and  pleasantly  occupies 
the  mind.  Late  at  night,  in  a  heated  room,  with  thin  clothing 
and  exciting  surroundings,  it  is  simply  a  dangerous  dissipation, 
ruinous  to  the  health,  alike  of  body  and  soul. 

*  This  muscle  is  attached  above  to  the  haunch-bone  or  ileum,  and  be- 
low to  the  knee-cap.  The  latter  bone  is  connected  by  a  strong  ligament 
with  the  tWa. 


IN    HYGIENIC    PHYSIOLOGY.  149 

15.  Why  can  ive  exert  greater  force  with  the  back  teeth 
than  with  the  front  ones  ? 

(See  Physiology,  p.  35.) 

The  lower  jaw  is  a  lever  of  the  second  class.  In  the  former 
case  the  resistance  to  be  overcome,  i.e.,  the  weight,  is  situated 
much  nearer  the  power. 

16.  Wliy  do  ive  lean  forward  ivhen  ive  wish  to  rise  from 

a  chair  ? 

(See  Popular  Physics,  p.  57.) 

In  order  to  bring  the  center  of  gravity  over  the  feet. 

17'  IVliy  does  the  projection  of  the  heel-bone  make 
ivalkiiig  easier  ? 

(See  Frontispiece,  and  also  Fig.  18  in  Physiology.) 
It  brings  the  power  further  from  the  fulcrum  or  weight. 

18.  Does  a  horse  travel  ivith  less  fatigue  over  aflat  than 
a  hilly  country  ? 

No.  The  variety  of  travel  in  a  hilly  country,  other  things 
being  equal,  tends  to  rest  the  horse,  and  enable  him  to  better 
endure  the  fatigue  of  the  journey. 

19.  Can  you  move  your  upper  jaw  ? 

All  the  bones  of  the  face,  except  the  lower  jaw,  are  firmly 
and  immovably  articulated  with  one  another  and  with  the  cra- 
nium.— LEIDY. 

20.  Are  people  naturally  right  or  left-handed  ? 

Many  persons  are  naturally  either  right  or  left-handed ;  but 
most  can  and  should  learn  to  use  either  hand  with  equal 
facility. 

21.  Why  can  so  few  persons  move  their  ears  by  the 
muscles  ? 

Perhaps  because  of  lack  of  practice ;  more  probably,  how- 
ever, the  muscles  (see  Physiology,  p.  53  and  Fig.  14)  are  de- 
veloped in  few  persons. 

22.  Is  the  blacksmith's  right  arm  healthier  than  the 
left? 


150  ANSWERS    TO    PRACTICAL     QUESTIONS 

By  no  means.  Strength  is  not  essential  to  health.  The 
right  arm  may  be  stronger,  but  the  functions  of  the  left  may 
be  as  active  and  well-performed. 

23.  Soys  often,  though  foolishly,  thrust  a  pin  into  the 
flesh  just  above  the  knee.     Why  is  it  not  painful  ? 

The  muscles  of  the  leg  there  end  in  tendons,  which  are  in- 
sensible. 

24.  Will  ten  minutes9  practice  in  a  gymnasium  answer 
for  a  day's  exercise  ? 

Spasmodic  or  violent  exercise  is  not  beneficial.  It  should  be 
comparatively  quiet,  gentle,  and  continuous  to  produce  the  best 
effect.  Moreover,  the  vitalizing  influences  of  the  sun  and  pure 
air  demand  that  we  should  exercise  out-of-doors. 

25.  Why  would  an  elastic  tendon  be  unfitted  to  trans- 
mit the  motion  of  a  muscle  ? 

Force  would  be  lost  by  its  transmission  through  an  elastic 
medium. 

26.  IVlien  one  is  struck  violently  on  the  head,  why  does 
he  instantly  fall  ? 

The  body  is  kept  erect  only  by  the  constant  exercise  of 
many  muscles.  These  perform  their  functions  through  the  un- 
conscious action  of  the  brain  and  spinal  cord.  A  blow  para- 
lyzes the  nervous  system,  the  muscles  at  once  cease  to  act,  and 
the  body  falls  by  its  weight. 

27 •  What  is  the  cause  of  the  difference  between  light 
and  dark  meat  in  a  fowl  ? 

The  amount  of  blood  which  circulates  through  different 
parts  of  the  body.  The  organs  of  a  fowl  which  are  used  the 
most  become  the  darkest. 

69— 1.  If  a  hair  be  plucked  out,  will  another  grotv  in 
its  place  ? 

Yes.  A  new  hair  will  always  grow  out  so  long  as  the  pa- 
pilla at  the  bottom  of  the  follicle  remains  uninjured. 


IN   HYGIENIC    PHYSIOLOGY.  151 

2.  Wliat  causes  the  hair  to  i( stand  on  end"  when  we 

are  frightened  ? 

(See  Physiology,  p.  53.) 

Many  of  the  unstriated  muscular  fibers  from  the  true  skin 
pass  obliquely  down  from  the  surface  of  the  dermis  to  the 
under  side  of  the  slanting  hair-follicles.  The  contraction  of 
these  fibers  erects  the  hairs,  and  by  drawing  the  follicles  to  the 
surface  and  drawing  in  a  little  point  of  the  skin,  produces  that 
roughness  of  the  integument  called  "goose-skin,"  or  Cutis  Anser- 
ina.  The  standing  on  end  of  the  hair  of  the  head,  as  the  re- 
sult of  extreme  fright,  may  be  partly  due  to  the  contraction  of 
such  fibers,  as  well  as  to  the  action  of  the  occipito-frontalis 
muscle. — CUTTER. 

3.  Why  is  the  skin  roughened  by  riding  in  the  cold  ? 

(See  Physiology,  p.  53 ;  also  Answer  to  Q  uestion  2.) 

4.  Why  is  the    back  of  a  washer-woman's  hand  less 
water-soaked  than  the  palm? 

The  difference  depends  upon  the  relative  abundance  of  the 
oil-glands  in  different  parts  of  the  body. 

5.  WJiat  would  be  the  length  of  the  perspiratory  tubes 
in  a  single  square  inch  of  the  palm,  if  placed  end  to  end  ? 

(See  Physiology,  p.  61.) 

The  length  of  the  perspiratory  tubes  differs  not  only  in  dif- 
ferent persons  but  in  different  parts  of  the  same  body.  Some 
authorities  estimate  the  average  length  at  \  of  an  inch,  while 
others— and,  generally,  later  authorities— give  only  -^  of  an  inch. 
If  we  assume  the  former  measurement,  we  have :  2,800  x  £  in. 
=  21^00  in.  =  58  ft.  4  in.  If  the  latter,  we  have  2,800xTV  in. 
=  Af$a  in.  =  14  ft.  7  in. 

6.  JVTiat  colored  clothing  is  best  adapted  to  all  seasons  ? 

(See  Physiology,  p.  67  ;  Popular  Physics,  p.  260.) 

Light-colored  clothing  is  cooler  in  summer  and  warmer  in 
winter. 

7.  What  is  the  effect  of  paint  and  powder  on  the  skin  ? 

(See  Physiology,  p.  62.) 


152  ANSWERS    TO    PRACTICAL     QUESTIONS 

They  fill  the  pores  of  the  skin,  and  thus  prevent  the  pas- 
sage of  the  perspiration.  Moreover,  they  often  contain  sub- 
stances which  are  poisonous,  and  being  carried  in  by  the  absorb- 
ents cause  disease. 

8.  Is  water-proof  clothing  healthful  for  constant  wear  ? 

No.  It  retains  the  insensible  perspiration  by  which  waste 
matter  is  being  constantly  thrown  off  from  the  system. 

9.  Why  are  rubbers  cold  to  the  feet  ? 

They  retain  the  insensible  perspiration.  The  moisture  which 
gathers  absorbs  the  heat  of  the  feet,  and  readily  conducts  it 
from  the  body. 

10.  Why  does  the  heat  seem  oppressive  ivhen  the  air  is 
moist  ? 

In  the  moisture-laden  atmosphere,  the  evaporation  of  the 
insensible  perspiration  from  the  surface  of  the  body  goes  on 
slowly.  The  heat,  which  would  otherwise  pass  off  through  the 
pores,  is  retained  in  the  system. 

11.  Why  is  friction  of  the  skin  invigorating  after  a 
cold  bath  ? 

(See  Physiology,  p.  64,  65.) 

The  friction  produces  heat,  expands  the  veins,  etc.,  on  the 
surface,  and,  calling  the  blood  in  that  direction,  produces  a 
vigorous  circulation.  In  other  words,  it  causes  a  reaction.* 

*  Strength  in  the  living  body  is  maintained  by  the  full  but  natural 
exercise  of  each  organ ;  and,  as  we  have  seen,  the  actions  of  these  por- 
tions of  the  nervous  system  is  made  dependent  upon  influences  conveyed 
to  them  by  the  sensitive  nerves  distributed  over  the  various  parts  of  the 
body.  And  among  these  the  nerves  passing  to  the  skin  are  the  chief.  The 
full  access  of  all  healthful  stimuli  to  the  surface,  and  its  freedom  from  all 
that  irritates  or  impedes  its  functions,  are  the  first  external  conditions  of 
the  normal  vigor  of  this  nervous  circle.  Among  these  stimuli,  fresh  air 
and  pure  water  hold  the  first  place.  Sufficient  warmth  is  second.  The 
great  and  even  wonderful  advantages  of  cleanliness  are  partly  referable  to 
the  direct  influence  of  a  skin  healthily  active,  open  to  all  the  natural 
stimuli,  and  free  from  morbid  irritation,  upon  the  nerve-centers  of  which 
it  is  the  appointed  excitant.  This  influence  is  altogether  distinct  from 
those  cleansing  functions  which  the  healthy  skin  performs  for  the  blood  ; 
and  in  any  just  estimate  of  its  value  is  far  too  important  to  be  over- 
looked.— HINTOJT. 


IN    HYGIENIC    PHYSIOLOGY.  153 

12.  Why  does  the   hair   of  domestic  animals  become 
roughened  in  ivinter  ? 

(See  Question  2.) 

It  is  a  wise  provision  of  Nature,  since  more  air — a  non-con- 
ductor of  heat — is  retained  by  the  hair,  and  thus  the  rough 
winter-coat  of  an  animal  is  warmer  than  its  smooth  summer- 
coat. 

13.  Why  do  fotvls  spread    their  feathers  before  they 

perch  for  the  night  ? 

(See  Question  12.) 

This  is  the  same  wise  provision  of  Nature  to  protect  the 
fowl  against  the  chilliness  of  the  night.  More  air  is  confined 
by  the  roughened  feathers,  and  thus  the  internal  heat  of  the 
bird  is  prevented  from  radiating. 

14.  Hoiv  can  an  extensive  burn  cause  death  by  conges- 
tion of  the  lungs  ? 

(See  Physiology,  p.  63.) 

The  insensible  perspiration  is  stopped  upon  the  burned  sur- 
face, and  the  excretions  are  sent  to  the  lungs,  which  are  over- 
worked and  overloaded  by  the  excess. 

15.  Why  do  ive  perspire  so  profusely  after  drinking  cold 
water  ? 

The  vital  organs  being  chilled  for  an  instant,  the  blood  is 
sent  to  the  surface,  a  reaction  is  produced,  the  skin  acts  more 
vigorously  as  an  excretory  organ,  and  the  insensible  perspira- 
tion is  thrown  off  more  rapidly. 

16.  What  are  the  best  means  of  preventing  skin  dis- 
eases, colds,  and  rheumatism  ? 

The  skin  should  be  kept  in  a  healthy  state  by  bathing,  rub- 
bing, etc.  Exposure  to  sudden  changes  of  temperature  should 
be  avoided  as  far  as  possible.  Flannel  worn  next  the  skin,  in 
all  seasons  of  the  year,  is  an  excellent  precaution  against  un- 
avoidable exposure. 

17 •  What  causes  the  difference  between  the  hard  hand 
of  a  blacksmith  and  the  soft  hand  of  a  woman  ? 

(See  Physiology,  p.  50.) 

The  varying  thickness  of  the  cuticle. 


154  ANSWERS    TO    PRACTICAL    QUESTIONS 

18.  Wliy  should  a  painter  avoid  getting  paint  on  the 

palm  of  his  hand  ? 

(See  Physiology,  p.  62.) 

19.  Why  should  we  not  use  the  soap  or  the  soiled  towel 
at  a  hotel  ? 

Because  of  the    danger  of  contracting  disease  through  the 

absorbents   of  the   skin.      (See  Physiology,  p.   62.)     There  is  a 

similar  danger   in  using   a  hair-brush   or  a  comb  at  a  barber 
shop. 

20.  Wliich  teeth  cut  like  a  pair  of  scissors  ? 

The  "back  teeth,"  as  we  commonly  call  them,  when  moved 
laterally,  cut  somewhat  in  this  way.  In  chewing  the  food,  all 
the  "front  teeth"  act  like  scissors,  as  may  be  readily  seen  by 
noticing  their  movements. 

21.  Which  teeth  cut  like  a  chisel? 

The  incisors,  or  four  front  teeth  of  each  jaw,  have  knife 
edges ;  the  canine  teeth  have  wedge-shaped  edges ;  the  bicus- 
pids and  molars  have  broader  crowns.  "We  can  work  the  jaws 
so  as  to  make  the  front  teeth  either  pierce  like  wedges  or  cut 
like  scissors. 

22.  Which  should  be  clothed  the  warmer,  a  merchant 
or  a  farmer  ? 

The  merchant  is  liable  to  more  sudden  and  violent  changes 
of  temperature,  and  his  body  is  less  likely  to  be  hardened  by 
exposure  and  habit  to  resist  them. 

23.  Why  should  we  not  crack  nuts  with  our  teeth  ? 

The  brittle  enamel  is  very  liable  to  crack,  and  once  broken 
can  never  be  restored. 

24.  Do  t he  edges  of  the  upper  and  lower  teeth  meet  ? 

(See  Question  21.) 

25.  Wlien  fatigued,  should  you  take  a  cold  bath  ? 

Certainly  not.  The  system  is  not  vigorous  enough  to  pro- 
duce a  reaction,  and  the  effect  might  be  dangerous. 


IN    HYGIENIC    PHYSIOLOGY.  155 

26.  Why  is  the  outer  surface  of  a  kid  glove  finer  than 
the  inner  ? 

This  illustrates  the  difference  in  texture  between  the  cutis 
and  cuticle ;  the  dermis  and  epidermis. 

27 •  WJiy  will  a  brunette  endure  the  sun's  rays  better 

than  a  blonde  ? 

(See  Physiology,  p  51.) 

The  skin  is  perhaps  of  a  coarser  texture,  and  not  so  sensi- 
tive to  heat.  May  it  not  be  also  that  the  black  pigment  ab- 
sorbs the  heat  and  radiates  it  again  rather  than  transmits  it 
directly  to  the  internal  organs  ?  It  has  also  been  suggested  that 
there  is  an  increased  flow  of  blood  in  the  darker  skin,  and 
hence  increased  perspiration. 

28.  Does  patent-leather  form  a  healthful  covering  for 
the  feet? 

No.  The  pores  of  the  leather  are  partly  filled,  and  hence 
the  insensible  perspiration  is  largely  restrained. 

29.  IVIiy  are  men  more  frequently  bald  than  women  ? 

This  is  to  some  extent  the  effect  of  the  close,  unventilated 
head-covering  commonly  worn  by  men. 

30.  On  what  part  of  the  head  does  baldness  commonly 
occur  ? 

On  that  part  most  fully  covered  by  the  hat  or  cap. 

31.  WJiat  does  the  combination  in  our  teeth  of  canines 
and  grinders  suggest  as  to  the  character  of  our  food  ? 

That  we  are  to  eat  a  mixed  diet  of  vegetable  and  animal 
food.* 

*  The  question  of  the  use  of  animal  or  vegetable  food  may  well  be  re- 
mitted to  the  arbitrament  of  nature,  as  expressed  in  the  desires ;  by  which 
it  would  be  victoriously  decided,  in  all  such  climates  as  ours,  in  favor  of 
the  flesh-eater.  But  the  sufficiency  of  vegetable  food,  if  widely  varied,  to 
maintain  health  and  even  strength,  is  not  to  be  questioned,  for  those  who 
like  it.  When  we  hear  that  the  ancient  Persians  lived  a  good  deal  on 
water-cress,  we  naturally  connect  in  our  minds  their  physical  inferiority 


156  ANSWERS    TO    PRACTICAL     QUESTIONS 

32.  la  a  staid,  formal  promenade  suitable  exercise? 

No.  There  is  an  intimate  relation  between  the  brain  and 
the  muscles.  The  mind  should  be  pleasantly  employed  to  ob- 
tain the  full  effect  of  any  exercise.*  The  sports  of  children  are 
often  the  very  perfection  of  healthful  gymnastic  exercises. 

33.  Is  there  any  danger  in  changing  the  warm  clothing 
of  our  daily  wear  for  the  thin  one  of  a  party  ? 

Very  great.  The  body  is  not  so  well  protected  as  usual 
against  a  sudden  change  of  temperature,  as  in  going  from  a 
heated  room  to  the  carriage,  and  a  cold  is  often  the  conse- 
quence. This  may  lay  the  foundation  of  fatal  disease. 

34.  Should  we  retain  our  overcoat,  shawl,  or  furs,  when 
we  come  into  a  warm  room  ? 

No.  The  body  will  become  over-heated,  the  pores  be  opened, 
and  the  skin  be  rendered  susceptible  to  the  change  of  tempera- 
ture when  we  return  into  the  open  air. 

with,  the  poverty  of  their  diet ;  but  finding,  on  the  other  hand,  that  the 
Romans,  in  the  best  period  of  the  Republic,  largely  sustained  themselves 
on  turnips,  and  that  degeneracy  came  in  as  turnips  went  out,  we  are  com- 
pelled to  reconsider  our  opinion.  In  brief,  an  exclusively  vegetable  food 
may  be  best  suited  to  those  by  whom  it  really  is  preferred.  Children  in 
this  respect  exhibit  the  greatest  difference ;  some,  with  manifest  advan- 
tage, eat  meat  in  large  quantity— others  can  hardly  be  prevailed  on  to  taste 
it,  and  yet  retain  perfect  vigor.  Similar  differences,  in  all  probability,  exist 
among  adults;  but  a  vegetarianism  self-imposed  against  the  promptings 
of  desire,  would  tend,  as  a  vigorous  writer  says,  to  make  us  "  not  the  chil- 
dren, but  the  abortions  of  Paradise."— HINTON. 

*  The  mental  operations,  like  all  others,  are  connected  with  changes  in 
the  material  of  the  body.  In  all  our  consciousness  the  chemical  tenden- 
cies of  the  substance  of  the  brain  come  into  play,  and  thus  a  chain  of 
action  is  set  up  which  extends  throughout  the  system.  The  influence  of 
these  brain-changes  is  felt  wherever  a  nerve  travels,  and  modifies,  invigor- 
ates, or  depraves  the  action  of  every  part.  Experience  gives  ample  proof 
of  this  fact  to  every  one,  as  in  the  sudden  loss  of  appetite  a  piece  of  bad 
news  will  cause,  or  in  the  watering  of  the  mouth  excited  by  the  thought 
of  food.  And  the  history  of  disease  abounds  in  evidence  of  a  similar  kind  : 
hair  becoming  gray  in  a  single  night  from  sorrow,  milk  poisoning  an  infant 
from  an  attack  of  passion  in  the  nurse,  permanent  discoloration  of  the 
skin  from  terror,  are  among  the  instances  on  record.— HINTON. 


7A    HYGIENIC    PHYSIOLOGY.  157 

35.  Which  should  bathe  the  oftener,  students  or  out- 
door laborers? 

This  depends  entirely  on  circumstances — the  amount  of  ex- 
ercise, the  individual  freedom  and  character  of  perspiration,  the 
state  of  the  system,  etc.  Each  case  must  be  decided  by  itself. 

36.  Is  abundant  perspiration  injurious  ? 

No.  It  removes  impure  matter  from  the  system,  and  hence 
may  be  beneficial.  It  may,  however,  weaken  the  body,  and 
frequent  hot  baths  should  therefore  be  taken  only  on  suitable 
medical  advice. 

37.  How  often  should  the  ablution  of  the  entire  body  be 
performed  ? 

For  the  preservation  of  perfect  health  there  should  be  daily 
morning  ablution  in  cold  or  cool  water,  using  soap  sparingly. 
A  warm  or  tepid  bath,  with  a  free  application  of  soap,  may 
advantageously  be  taken  once  a  week,  followed  by  a  dash  of 
cool  water.  It  is  well  for  children  and  delicate  persons  to 
stand  in  warm  water,  having  the  cold  water  in  an  extra  tub  or 
basin.  They  can  then,  with  a  large  sponge,  dash  the  cold 
water  freely  over  their  bodies,  and  get  the  full  tonic  effect  of 
the  cold  bath  without  the  coldness  or  discomfort  which  might 
otherwise  ensue.  A  cold  bath  should  always  be  quickly  per- 
formed, accompanied  by  vigorous  rubbing  to  insure  the  reac- 
tion. Children  especially  should  be  thoroughly  rubbed  and  com- 
pletely dried.  Above  all,  let  the  daily  wash  be  a  delight,  and 
not  a  dread,  to  the  little  ones.  A  reluctant  bath,  with  a  hasty 
dismissal,  leaving  the  skin  wet,  the  blood  chilled,  and  the  spirits 
depressed,  not  only  inflicts  upon  the  helpless  and  unhappy 
child  a  needless  misery,  but  will  be  likely  to  result  in  chapped 
skin  and  chronic  catarrh,  if  in  nothing  worse. 

38.  Why  is  cold  tvater  better  than  warm  for  our  daily 
ablution  ? 

(See  Physiology,  p.  64.) 

The  daily  repetition  of  the  cold  bath  renders  the  system 
less  sensitive  to  changes  in  atmospheric  temperature,  the  re- 
verse being  the  case  with  the  warm  bath.  Still,  it  should  be 
said  that  not  every  one  is  able  to  endure  the  cold  bath.  If  the 


158  AXSWESS    TO    PRACTICAL     QUESTIONS 

skin  remains  cold  and  blue  in  spite  of  friction,  it  shows  that 
the  reaction  has  not  taken  place,  in  which  case  the  bath  is  an 
injury.  Or,  if  for  some  time  after  the  bath  the  bather  feels 
languid  and  weary,  it  indicates  that  the  reaction  is  too  much 
for  his  nervous  system.  But,  in  most  cases,  if  the  habit  is 
formed  by  beginning  first  with  tepid  water,  decreasing  the  tem- 
perature gradually,  morning  by  morning,  until  the  bather  in- 
ures himself  to  the  coldest  water,  the  shock  and  the  reaction 
will  be  a  luxury  he  will  not  willingly  abandon.  In  this  con- 
nection it  may  be  said  that,  as  water  is  a  better  conductor  of 
heat  than  air,  water  at  a  temperature  of  75°  or  80°  will  seem 
cold  to  most  persons  (the  normal  temperature  of  the  body  being 
about  98°  Fahr.),  though  an  atmosphere  of  that  degree  would 
seem  warm.  The  temperature  of  the  room  should  always  be 
higher  than  that  of  the  water. 

39.   llJiy  should  our  clothing  always  fit  loosely  ? 

(See  Physiology,  pp.  14,  67,  96.) 

Any  thing  that  impedes  circulation  is  injurious.  Loose  un- 
der-clothing is  warmer  in  winter  than  tight  under-clothing,  on 
account  of  the  stratum  of  air  between  the  body  and  the  gar- 
ment. (See  Question  12.)  The  effects  of  tight-lacing  are  well 
known.*  Too  close-fitting  sleeves  interfere  with  the  venous  cir- 
culation of  the  arm,  and  tend  to  make  the  fingers  cold  and 
blue ;  while  the  pressure  upon  the  nerves,  which  lie  not  far 

*  The  evil  effects  of  tight-lacing  are  not  all  nor  always  in  the  future. 
Signs  of  distress  are  often  quickly  apparent ;  the  nose  purples,  the  upper 
bowels  emit  croaking  sounds,  while  the  lower  become  unnaturally  protu- 
berant ;  the  womb  falls,  and  the  breathing  and  the  circulation  of  blood 
are  so  hindered  as  often  to  bring  on  palpitations  of  the  heart  and  faint- 
ing ;  especially  after  a  full  meal  or  in  a  close  and  sultry  atmosphere.  The 
long-continued  and  tight  pressure  of  corsets  also  wastes  and  impairs  the 
natural  strength  of  the  muscles  of  the  back;  so  that  without  the  usual 
lacing  there  is  a  most  uncomfortable  feeling  of  weakness.  The  circulation 
of  the  blood  in  the  lower  part  of  the  lungs,  from  the  severe  compression 
imposed  upon  them,  becomes  in  an  almost  stagnant  condition,  producing 
languor  and  a  painful  sense  of  lassitude.  Continue  this  constraint,  and 
the  cell-life  of  the  lungs,  liver,  and  stomach  becomes  permanently  im- 
paired, laying  a  sure  foundation  for  disease  in  these  parts  whenever  the 
constitutional  strength  and  vigor  begin  to  fail.— The  Ten  Laws  of  Health,  J. 
B.  BLACK. 


IN    HYGIENIC    PHYSIOLOGY.  159 

below  the  skin,  induce  neuralgia  and  numbness  in  the  fingers. 
A  rigid  constriction  about  the  arm-pit  will  frequently  result  in 
a  swollen  hand.  Tight  elastics  should  never  be  worn  upon  the 
lower  limbs.  Aside  from  all  the  discomforts  and  maladies  at- 
tendant upon  the  wearing  of  tight  garments,  the  natural  ease 
and  grace  of  bodily  movement  are  always  more  or  less  ob- 
structed. 

4O.  Why  should  we  take  special  pains  to  avoid  clothing 
that  is  colored  by  poisonous  dye-stuffs  ? 

(See  Physiology,  p.  62.) 

Because  the  particles  of  the  poisonous  coloring  are  liable  to 
be  absorbed  by  the  skin,  and  thus  taken  into  the  system.  The 
dangerous  agent  is  usually  arsenic,  which  is  employed  in  dyeing 
bright  reds,  magentas,  aniline  reds,  and  certain  greens.  Par- 
ticular care  should  be  taken  in  the  selection  of  hose.  Unfortu- 
nately, the  pure  white  stocking  has  gone  out  of  style,  though 
hygienically  it  is  greatly  preferable  to  the  highly  (often  poison- 
ously)  dyed  one  that  has  succeeded  to  fashionable  favor. 

4:1.  WJiat  general  principles  should  guide  us  as  to  the 
length  and  frequency  of  baths  in  salt  or  fresh  water  ? 

(See  Physiology,  pp.  66,  291.) 

Sea  or  river  baths  should  never  be  prolonged  to  the  extent 
of  sensible  fatigue,  and  consequent  inability  of  reaction.  A 
daily  swim  taken  before  breakfast,  and  limited  to  twenty  min- 
utes at  the  outside,  is  to  most  people  the  best  of  tonics.  Per- 
sons with  pale  skins  (technically  termed  anaemic,  or  bloodless), 
or  those  who  are  suffering  from  heart  disease,  should  not  at- 
tempt sea  or  river  bathing,  or,  indeed,  any  cold  bath,  except 
under  medical  advice. 

42.  What  is  the  beneficial  effect  of  exercise  upon  the 
functions  of  the  skin  ? 

(See  Physiology,  p.  62;  also  note,  p.  42.) 

Increased  muscular  action  calls  for  an  extra  supply  of  blood. 
The  heart  responds  by  more  rapid  beating,  the  lungs  take  in 
more  oxygen,  and  the  bodily  heat  is  heightened.  To  dispose  of 
this  superfluous  warmth,  the  oil  and  perspiratory  glands  are 
stimulated  to  greater  activity,  the  impurities  which  naturally 


160  ANSWERS    TO    PRACTICAL     QUESTIONS 

escape  from  the  body  by  this  avenue  are  hastened  in  their  exit, 
and  the  skin  itself  becomes  soft  and  moist. 

43.  How  can  ive  best  show  our  admiration  and  respect 
for  the  human  body  ? 

By  conscientiously  observing  all  the  laws  of  physical  hy- 
giene, as  well  as  moral  purity. 

44.  IVTiy  is  the  scar  of  a  severe  wound  upon  a  negro 
sometimes  white  ? 

Because  the  cells  containing  the  pigment  or  coloring  matter 
were  destroyed  by  the  severity  of  the  wound,  and  have  not 
been  restored. 

99 — !•  What  is  the  philosophy  of  the  "change  of 
voice  "  in  a  boy  ? 

Up  to  the  age  of  fourteen  or  fifteen,  there  is  little  or  no 
difference  in  point  of  size  between  the  larynx  of  a  boy  and 
that  of  a  girl ;  but  subsequently  the  former  grows  proportion- 
ately larger,  so  that  at  last,  in  the  adult  male,  the  vibrating 
parts  or  vocal  cords  are  necessarily  longer  than  in  the  female. 
They  are  also  undoubtedly  thicker,  perhaps  even  coarser  in 
structure.  From  all  these  circumstances  the  adult  male  voice 
is  stronger,  louder,  and  of  lower  pitch  than  the  weaker  and 
higher  vocal  range  accomplished  by  the  female  larynx. 

The  cause  of  the  difference  in  quality  of  the  voice,  known 
as  its  timbre,  is  not  well  known  ;  but  it  must  undoubtedly  be 
dependent  on  physical,  that  is  to  say,  structural  peculiarities  in 
some  part  of  the  laryngeal  apparatus. 

The  production  of  the  different  notes  within  the  compass  of 
any  one  individual  depends  upon  alterations  in  the  length  and 
state  of  tension  of  the  vocal  cords,  and  on  their  degree  of  prox- 
imity or  separation  from  one  another.  The  higher  notes  require 
the  vocal  cords  to  be  comparatively  shorter,  tighter,  and  more 
closely  approximated  together ;  while  the  lower  notes  demand 
opposite  conditions.  A  high  note,  furthermore,  implies  greater 
rapidity  in  the  movement  of  the  air  through  the  glottis ;  but 
the  quantity  of  air  passing  is  larger  during  the  production  of  a 
low  note. 


IN    HYGIENIC    PHYSIOLOGY.  161 

The  volume  or  loudn&ss  of  the  voice  depends  mainly  on  the 
combination  of  quantity  of  air  with  greater  force  of  expulsion. 
Loudness,  with  clearness,  also  demands  a  peculiar  resonance 
up  in  the  nasal  cavities  and  sinuses.  Lastly,  the  unnatural  or 
falsetto  voice  seems  also  to  be  produced  by  some  tensive  change 
effected  in  the  upper  part  of  the  pharynx  at  the  back  of  the 
nose :  hence  it  is  called  by  singers  the  head  voice,  in  contradis- 
tinction to  the  ordinary,  or  chest  voice. — MARSHALL. 

2.  Why  can  ive  see  our  breath  on  a  frosty  morning  ? 

The  vapor  of  the  breath  is  condensed  by  the  cold  air. 

3.  When  a  laiv  of  health  and  a  laiv  of  fashion  conflict , 
which  should  ^ve  obey  ? 

It  depends,  of  course,  whether  we  prefer  to  be  fashionable 
or  to  be  healthy,  to  obey  man  or  God.  With  too  many  people 
the  former  is  of  far  greater  importance,  and  in  selecting  an 
article  of  dress,  few  ask  or  think  about  the  latter.  The  conse- 
quence is  seen  in  the  weakened  frame,  the  prevalence  of  dis- 
ease, and  the  shortened  life.  God's  laws  written  in  our  bodies 
can  not  be  violated  with  impunity. 

4.  If  we  use  a  "  bunk  "  bed9  sJioidd  we  pack  away  the 
clothes  when  ive  first  rise  in  the  morning  ? 

No.    They  should  first  be  thoroughly  aired. 

5.  Why  should  a  clothes-press  be  ivcll  ventilated? 

The  clothes  naturally  contain  the  products  of  the  insensible 
perspiration,  which  passing  off,  pollute  the  air  of  the  closet. 

6.  Sliould  the  weight  of  our  clothing  Jiang  from  the 
tvalst  or  the  shoulder  ? 

From  the  shoulder,  so  as  to  avoid  the  constriction  of  the 
compressible  organs  in  the  abdomen. 

7.  Describe    the   effects    of   living    in    an    overheated 
room. 

(1)  The  body  becomes  moro  sensitive  to  change,  and  the 
susceptibility  to  colds  is  greatly  increased  ;  (2)  the  dry,  heated 
air  abstracts  the  moisture  from  the  skin,  rendering  it  dry,  hard, 
and  incapable  of  performing  its  normal  functions. 


162  ANSWERS    TO    PRACTICAL    QUESTIONS 

8.  Wliat  habits  impair  the  power  of  the  lungs? 

Above  all  others,  those  of  a  leaning  posture,  tight-lacing, 
and  ill-ventilation. 

9.  For  fall9  easy  breathing  in  singing,  should  ive  use 
the  diaphragm  and  lower  ribs  or  the  upper  ribs  alone  ? 

Nearly  all  the  inspirations  are  effected  by  the  movements 
of  the  diaphragm  and  the  inferior  ribs  only.  From  time  to 
time  a  deeper  and  more  complete  inspiration  causes  the  thorax 
to  rise,  not  simultaneously,  but  successively  at  the  base,  then 
at  the  apex.  In  the  first  case  the  respiration  is  diaphragmatic; 
when  the  lower  and  middle  ribs  are  raised,  it  is  termed  lateral; 
and,  lastly,  when  the  first  rib  and  clavicle  take  part  in  the 
movement,  it  is  costo-superior  or  clavicular.  In  diaphragmatic 
respiration,  as  M.  Mandl  has  observed,  the  larynx  is  immov- 
able, the  inspiration  is  easy,  without  effort,  and  permits  exer- 
tion in  singing  or  in  gymnastics  for  a  long  time  and  without 
fatigue.  On  the  contrary,  persons  who  respire  principally  by 
the  upper  ribs  are  easily  fatigued,  and  very  soon  out  of  breath. 
This  is  seen  in  women  when  the  corset  compresses  the  base  of 
the  chest,  and  in  singers  who  adopt,  on  erroneous  principles, 
the  bad  habit  of  clavicular  respiration.  In  this  last  method  of 
inspiration  the  larynx  is  drawn  down  by  the  contraction  of  the 
external  muscles,  and  its  action  becomes  painful.  The  effort  of 
the  inspiratory  muscles  rapidly  induces  fatigue,  and  the  inspi- 
ration, always  incomplete,  becomes  also  more  frequent.  Dia- 
phragmatic respiration  is  practiced  by  mountaineers,  gymnasts, 
and  skillful  singers — a  habit  induced  either  by  instinct,  or  a 
well-directed  education. —  Wonders  of  the  Human  Body. 

10.  Why  is  it  better  to  breathe  through  the  nose  than 
the  mouth  ? 

The  air  passing  through  the  nostrils  becomes  filtered  of  its 
coarse  impurities,  and  the  chill  is  taken  off  before  it  strikes 
against  the  tender,  mucous  surfaces  of  the  larynx. 

11.  Why  should  not  a  speaker  talk  while  returning 
home  on  a  cold  night  after  a  lecture  ? 

The  cold  air  will  strike  against  the  vocal  apparatus  when 
inflamed  and  peculiarly  sensitive. 


IN    HYGIENIC    PHYSIOLOGY.  163 

12.  What  part  of  the  body  needs  the  loosest  clothing  ? 

The  abdomen ;  because  of  the  delicate  organs  within,  un- 
protected by  a  bony  covering. 

13.  What  part  needs  the  warmest  ? 

The  feet,  because  they  are  furthest  from  the  center  of  heat 
and  motion,  and  most  exposed  to  cold  and  wet :  and  the  neck 
and  shoulders,  since  here  are  located  the  delicate  organs  of 
voice  and  respiration. 

14.  Why  is  a  6i  spare  bed99  generally  iinhealthful  ? 

Because  it  is  apt  to  be  damp  and  unventilated. 

15.  Is  tit  ere  any  good  in  sighing  ? 

(See  Physiology,  p.  82.) 
It  probably  brings  up  the  "arrears"  of  respiration. 

10.  Should  a  hat  be  thoroughly  ventilated?    Hotv? 

1.  Certainly,  as  the  heated,  foul  air  is  injurious.  2.  Several 
openings  should  be  made  on  the  sides  near  the  band.  A 
single  hole  at  the  top  is  quite  insufficient  for  ventilation. 

1 7.  Why  do  the  lungs  of  people  who  live  in  cities  become 
of  a  gray  color  ? 

Probably  because  of  the  deposition  of  carbonaceous  particles 
which  penetrate  the  substance  of  the  tissues.  The  coloring  is 
permanent,  like  tattooing,  where  India-ink  is  pricked  beneath 
the  skin. 

18.  Hoiv  would  tfbu  convince  a  person  that  a  bedroom 
should  be  aired  ? 

Take  him  from  the  fresh,  pure,  invigorating  out-door  at- 
mosphere into  the  close,  depressing  air  of  the  bedroom,  when 
first  vacated  in  the  morning,  and  his  sense  of  smell  will  satisfy 
him  of  the  need  of  ventilation. 


19.   IVTiat  persons  are  tnost  liable  to  catarrh 9  consump- 

w,  etc.  ? 

(See  Physiology,  p.  85.) 

The  victims  of  lung-starvation. 


164  ANSWERS    TO    PRACTICAL     QUESTIONS 

20.  If  a  person  is  plunged  under  water,  will  any  enter 
his  lungs  ? 

No.  The  epiglottis  will  close  involuntarily,  and  prevent  the 
admission  of  water. 

21.  Are  bed- curtains  healthful  ? 

No.  They  prevent  the  free  circulation  of  the  air,  and  con- 
fine the  waste  products  thrown  off  from  the  body. 

22.  Why  do  some  persons  take  "  short  breaths  "  after  a 
meal? 

The  distention  of  the  stomach  prevents  the  free  action  of 
the  lungs.  If  such  persons  arc  not  given  to  gluttony,  the  lungs 
are  small  or  the  other  organs  misplaced. 

23.  What  is  the  special  value  of  public  parks  ? 

They  bring  fresh  air,  nunshine,  green  grass  and  trees 
within  the  reach  of  all.  They  are  truly  the  "breathing-holes 
of  a  city."  They  arc  thus  of  incalculable  benefit  both  on  ac- 
count of  their  sanitary  and  moral  influence. 

24:.  Can  a  person  become  used  fo  bad  air,,  so  that  it  ivill 
not  injure  Jiini  ? 

The  system  may  come  to  endure  without  complaint,  but, 
sooner  or  later,  it  never  fails  to  inflict  full  punishment  for  the 
infraction  of  nature's  laws. 

25.   Why  do  ive  gape  when  tec  arc  sleepy  ? 

(See  Question  15.) 

The  stretching  of  the  nerves  may  perhaps  serve  to  restore 
the  equilibrium  of  the  nervous  influence,  disturbed  by  the  at- 
tention being  fixed  during  the  day  upon  some  absorbing  occu- 
pation. 

26.  Is  a  fashionable  waist  a  model  of  art  in  sculpture 
or  painting  ? 

The  Venus  of  Milo,  in  the  Louvre  at  Paris,  is  the  beau- 
ideal  of  symmetry  and  beauty,  yet  the  form  indicates  not  a 
"wasp-waist,"  but  the  full,  free,  flowing  outlines  of  nature. 
The  sculptor  and  painter  in  copying  the  human  figure  can 
make  no  improvement  on  its  Divine  Maker. 


IN   HYGIENIC    PHYSIOLOGY.  165 

27.  Should  afire-place  be  closed? 

(See  Physiology,  p.  99.) 
No.    It  is  a  most  efficient  means  of  ventilation. 

28.  Why  does  embarrassment  or  fright  cause  a  stam- 
merer to  stutter  still  more  painfully  ? 

Stuttering  is  mainly  a  nervous  disorder,  and  hence  any  ex- 
citement tends  to  increase  the  impediment  of  the  speech. 

29.  In  the  organs  of  voice,  what  parts  have  somewhat 
the  same  office  as  the  case  of  a  violin  and  the  sounding- 
board  of  a  piano  ? 

(See  Popular  Physics,  p.  186.) 

The  pharynx,  the  mouth,  and  the  nasal  passages  all  act  by 
resonance  to  modify  the  voice. 

30.  Why  should  tve  be  careful  not  to  "  take  the  breath9' 
of  a  sick  person  ? 

Because,  in  this  manner,  special  disease  germs  may  be  di- 
rectly transferred  from  the  lungs  of  the  sick  person  into  our 
own.  It  is  well  never  to  "take  the  breath"  of  any  person, 
sick  or  well,  since  impurities  are  constantly  passing  off  from 
every  human  system  through  the  avenue  of  the  lungs. 

31.  What  special  care  should  be  taken  with  regard  to 
keeping  a  cellar  clean  ? 

The  walls  and  floor  should  be  free  from  moisture,  and  any  ac- 
cumulation whatever  of  dust  or  refuse.  There  should  be  not  only 
some  means  of  constant  ventilation,  but  the  windows  ought  fre- 
quently to  be  opened  to  full  currents  of  air  from  without. 
Vegetables  should  never  be  allowed  to  decay  in  the  cellar.  In  these 
days  of  furnaces,  when,  in  addition  to  the  ordinary  upward 
travel  of  cellar  odors,  the  sides  of  the  registers  in  the  rooms 
above  afford  a  direct  means  of  ascent  for  all  the  foul  or  stag- 
nant air  that  may  lurk  below,  the  basement  should  be  the 
sweetest  and  most  immaculate  portion  of  the  house. 

32.  How  is  the  air  strained  as  it  passes  into  the  lungs  ? 

The  constant  motion  of  the  cilia,  which  line  the  air-pas- 
sages, produces  an  outward  current,  which  arrests  and  expels 


166  ANSWERS    TO    PRACTICAL     QUESTIONS 

intrusive   particles   that,   swept  inward    by  the   breath,   would 
otherwise  pass  into  the  lungs. 

33.  Can  one  really  if  draw  the  air  into  his  lungs  "  ? 

(See  Physiology,  p.  80.) 

Strictly  speaking,  no.  In  the  act  of  inspiration  we  so  con- 
tract the  muscles  as  to  enlarge  the  cavity  of  the  chest,  thus  re- 
ducing the  pressure  upon  the  lungs,  upon  which  the  external 
atmosphere,  in  seeking  an  equilibrium,  rushes  in  to  fill  the 
space. 

34.  How  often  do  we  breathe  ? 

Ordinarily  about  eighteen  times  a  minute. 

35.  Describe  some  approved  method  of  ventilation. 

(See  Physiology,  p.  92.) 

36.  What  is  at  once  the  floor  of  the  chest  and  the  roof 
of  the  abdom,en  ? 

The  diaphragm. 

37.  What  would  you  do  in  case  of  apparent  death  by 
drowning  or  by  coal-gas  ? 

(See  Physiology,  p.  264.) 

38.  What  would  you  do  in  case  of  croup,  'while  the 
doctor  was  coming  ? 

(See  Physiology,  p.  260.) 

39.  How  would  you  treat  a  severe  burn  ? 

(See  Physiology,  p.  257.) 

40.  Describe  the  various  ways  in  which  the  water  in  a 
well  is  liable  to  become  unwholesome. 

In  towns  and  cities  organic  matter,  solid  or  in  solution, 
permeates  the  soil  to  the  depth  of  several  feet,  and  shallow 
wells  are  therefore  quite  certain  to  be  polluted,  as  any  earth 
used  constantly  as  a  filter  will,  in  the  course  of  years,  lose  its 
purifying  properties.  Wells,  too,  are  often  placed  in  dangerous 
proximity  to  cemeteries,  cess-pools,  barn-yards,  vaults,  etc.,  and 
in  many  cases  receive  direct  drainage  from  these  pestilential 
sources.  Impurities  will  collect  in  wells  that  are  not  periodic- 


IN   HYGIENIC    PHYSIOLOGY.  167 

ally  cleaned,  especially  if  the  water  in  them  is  not  freely  ex- 
posed to  the  oxygen  of  the  air.  If  one  must  depend  upon  well- 
water,  the  safest  reliance  is  upon  a  deep-driven  well. 

1 47 — !•  Why  does  a  dry,  cold  atmosp7iere  favorably 
affect  catarrh  ? 

It  tends  to  diminish  inflammation  in  the  mucous  membrane 
lining  the  nose  and  nasal  passages. 

2.  Why  should  we  put  on  extra  covering  when  we  lie 
down  to  sleep  ? 

The  respiration  and  the  circulation  are  then  less  active. 
The  fire  in  our  corporeal  stoves  being  low,  we  need  extra  cov- 
ering to  preserve  the  warmth  of  the  body. 

3.  Is  it  well  to  throiv  off  our  coats  or  shawls  when  we 
come  in  heated  from  a  long  walk? 

No.  "We  need,  instead,  to  put  on  extra  clothing  at  such  times 
to  keep  the  body  from  cooling  too  rapidly.  The  best  hygienic 
teachers  commend  the  throwing  of  a  shawl  about  the  shoulders 
whenever  we  sit  down  to  rest  after  fatiguing  labor. 

4.  JFliy  are  close-fitting  collars  or  neck-ties  injurious  ? 

They  impede  both  respiration  and  circulation. 

5.  Which  side  of  the  heart  is  the  more  liable  to  inflam- 
mation ? 

The  left ;  because  that  contains  the  red  blood  just  oxygenated 
in  the  lungs. 

6.  What  gives  the  toper  his  red  nose  ? 

(See  Physiology,  p.  126.) 

The  congested  state  of  the  capillaries. 

7.  Why  does  not  the  arm  die  when  the  surgeon  ties  the 
principal  artery  leading  to  it  ? 

The  anastomoses  of  the  arteries  enable  a  collateral  circula- 
tion to  be  established,  whereby  blood  is  supplied  to  the  arm. 

8.  Wlien  a  fowl  is  angry,  ivhy  does  its  comb  redden^ 


168  ANSWERS    TO    PRACTICAL    QUESTIONS 

Because  an  extra  quantity  of  blood  is  thrown  into  that  part 
of  the  body. 

9.  Why  does  a  fat  man  endure  cold  better  than  a  lean 
one? 

Fat  is  a  good  non-conductor  of  heat,  and  helps  to  preserve 
the  uniform  temperature  of  the  body. 

1 0.  IVJiy  does  one  become  thin  during  a  long  sickness  ? 

By  absorption,  the  fat  of  the  body  is  taken  up  and  used  to 
supply  the  wants  of  the  system.  The  old  flesh  being  renewed 
with  new,  vigorous  material,  a  person  often  has  better  health 
after  such  a  wasting  sickness  than  previous  to  it. 

11.  If 'hat  would  you  do  if  you  should  come  home  "  ivet 
to  the  skin  "  ? 

One  should  (1)  go  into  a  warm .  room  ;  (2)  remove  all  wet 
garments ;  (3)  if  chilled,  take  a  hot,  full  or  foot  bath,  and  by 
gentle  friction  restore  the  circulation  ;  (4)  put  on  dry  clothing. 

12.  Wit  en  the  cold  air  strikes  the  face,  why  does  it  first 
blanch  and  then  flush  ? 

The  muscles  and  blood-vessels  of  the  surface  are  contracted 
by  the  cold,  and  the  blood  is  driven  back  toward  the  heart. 
The  reaction  which  ensues  forces  the  blood  again  toward  the 
skin,  and  this  flushes  with  the  incoming  tide.  The  face  is 
therefore  first  whitened  and  then  reddened. 

13.  What  must  be  the  effect  of  tight  lacing  upon  the 
circulation  of  the  blood  ? 

It  must,  by  contracting  the  blood-vessels,  impede  the  flow 
of  the  blood,  and  by  decreasing  the  quantity  furnished  the 
various  organs,  injure  their  action.  Thus,  finally,  it  will  im- 
pair the  quality  of  the  blood. 

14.  Do  you  knoiv  the  position  of  the  large  arteries  in 
the  limbs,  so  that  in  case  of  accident  you  could  stop  the 
floiv  of  blood  ? 

These  can  be  located  by  examining  the  cut  in  Physiology, 
page  104,  or  any  good  chart  of  the  circulation. 


/JV    HYGIENIC    PHYSIOLOGY.  169 

15.  When  a  person  is  said  to  be  "  good-hearted,"  is  it 
a  physical  truth  ? 

The  expressions,  large-hearted,  good-hearted,  etc.,  are  re^ 
mains  of  the  old  idea  that  the  affections  are  located  in  the 
heart  rather  than  in  the  brain — the  seat  of  the  mind  and  all  its 
attributes.* 

16.  Why  does  a  hot  foot-bath  often  relieve  the  head- 
ache ? 

(Sec  Physiology,  p.  126.) 

It  withdraws  blood  from  the  head,  and  so  relieves  the  con- 
gested state  of  that  organ. 

f» 

17 '•  IVTiy  does  the  body  of  a  drowned  or  strangled  per- 
son turn  blue  ? 

*  In  connection  with  this  subject,  the  following  from  a  recent  article 
by  Dr.  Wm.  A.  Hammond,  will  be  found  of  interest:  "In  the  very  earliest 
times  of  which  we  have  any  record,  and  even  at  the  present  day  among 
barbarous  nations,  the  idea  existed  that  the  brain  was  not  the  only  organ 
concerned  in  the  production  of  mind.  .  .  .  Doubtless,  its  origin  was  due  to 
the  fact  that,  under  the  influence  of  certain  emotions,  there  are  disturb- 
ances in  the  organs  with  which  they  are  associated.  Thus,  love  quickens 
the  action  of  the  hearb ;  mental  depression  or  anger  deranges  the  liver ; 
and  pity  produces  what  is  sometimes"  called  '  a  sinking  feeling '  at  the  pit 
of  the  stomach.  It  has  been  customary  with  modern  writers  to  regard 
these  disturbances  as  being  the  effects  of  emotions  that  originated  in  the 
brain,  and  not  as  indicating  that  the  organs  in  which  they  are  felt  have 
any  thing  to  do  with  the  evolution  of  love,  or  anger,  or  fear,  or  compassion, 
or  any  other  passion  or  feeling.  .  .  .  The  idea  has  become  so  widely  spread 
among  educated  persons  that  the  brain  is  the  only  organ  of  the  body  that 
has  any  direct  relation  as  a  generator  with  the  mind,  that  it  seems  like  a 
tremendous  blow  at  the  system  of  existing  facts  to  attempt  to  take  from  it 
any  of  its  power.  But  it  is  only  recently  that  physiologists  and  patholo- 
gists  are  beginning  to  make  a  thorough  investigation  into  that  great  divis- 
ion of  the  nervous  system  consisting  of  the  sympathetic  nerves  and  their 

ganglia Now,'  it    is    not  unreasonable   to   suppose    that    these 

masses  of  the  tissue  in  question,  that  are  placed  around  the  heart,  the 
liver,  the  spine,  and  other  organs,  and  in  vast  number  in  their  substance, 
have  some  influence  in  causing  the  production  of  those  emotions  that 
make  themselves  felt  in  the  parts  of  the  body  with  which  former  univer- 
sal beliefs,  and  our  present  forms  of  speech,  have  associated  them.  We 
find,  too,  as  an  additional  fact  in  support  of  this  view,  that  in  certain 
mental  affections,  characterized  by  great  emotional  disturbances,  these 
ganglia  are  in  various  parts  of  the  body  the  seats  of  disease." 


170  ANSWERS    TO    PRACTICAL     QUESTIONS 

The  blood  is  not  purified  in  the  lungs,  and  so  blue  or  ve- 
nous blood  fills  the  vessels. 

18.  What  are  the  little  "kernels"  in  the  arm-pits  ? 

(See  Physiology,  p.  125.) 

They  are  the  lymphatic  glands,  which  sometimes  become 
swollen. 

19.  When  we  are  excessively  ivarm,  would  the  ther- 
mometer show  any  rise  of  temperature  in  the  body  ? 

(See  Physiology,  p.  120,  note.) 

Probably  not.  In  health,  the  average  temperature  of  the 
body  does  not  vary  mere  than  two  degrees. 

20.  What  forces  besides  that  of  the  heart  aid  in  pro- 
pelling the  blood  ? 

(See  FLINT'S  Physiology— The  Circulation ;  CUTLER'S  Analytic  Anatomy,  etc  . 
p.  166,  etseq.) 

The  elasticity  of  the  arteries  and  the  veins,  the  force  of 
capillary  attraction  in  the  capillaries,  etc. 

21.  iriiy  can  the  pulse  be  best  felt  in  the  ivrist  ? 

It  is,  in  general,  a  mere  matter  of  convenience.  We  can 
feel  it  not  only  in  the  radial  artery  at  the  wrist,  but  in  the 
carotid  of  the  neck,  the  temporal  of  the  forehead,  the  popliteal* 
in  the  inner  side  of  the  knee,  etc. 

22.  Wliy  are  starving  people  exceedingly  sensitive  to 
any jar ? 

The  marrow  of  the  bones  is  absorbed,  and  hence  the  shock 
of  a  jar  is  unbroken.  The  nervous  system  is  also  weakened  by 
the  general  prostration. 

23.  Why  will  friction,  an  application  of  horse-radish 
leaves ,  or  a  blister  relieve  internal  congestion  ? 

They  bring  the  blood  to  the  surface  of  the  body,  and  so  re- 
lieve the  internal  organ. 

*  If  the  hollow  of  the  knee  of  one  leg  be  allowed  to  rest  upon  the  knee 
of  the  other  one,  it  may  be  remarked  that  the  point  of  the  suspended  foot 
moves  visibly  up  and  down  at  each  beat  of  the  pulse. 


IN  HYGIENIC    PHYSIOLOGY.  171 

24.  Why  are  students  very  liable  to  cold  feet  ? 

Because  the  tendency  of  the  blood  is  toward  the  head,  to 
supply  the  waste  in  that  part  of  the  body. 

25.  Is  the  proverb  that  "  blood  is  thicker  than  water 7f 
literally  true  ? 

(See  DBAPEB'S  Human  Physiology,  p.  112.) 

The  specific  gravity  of  the  blood  varies  from  1.050  to  1.059. 

26.  What  is  the  effect  upon  the  circulation  of  6(  holding 
the  breath"? 

The  blood  is  not  oxygenated,  the  products  of  waste  accumu- 
late in  the  system,  the  circulation  is  impeded,  the  blood-vessels 
become  distended,  and  are  liable  to  burst,  while  all  the  delicate 
organs,  especially  the  brain,  are  oppressed  by  congestion. 

27.  Which  side  of  the  heart  is  the  stronger  ? 

The  left,  which  drives  the  blood  to  the  extremities. 

28.  Hoiv  is  the  heart  itself  nourished? 

The  coronary  arteries  springing  from  the  aorta  just  after 
its  origin,  carry  blood  to  the  muscular  walls  of  the  heart:  the 
venous  blood  comes  back  through  the  coronary  veins,  and 
empties  directly  into  the  right  auricle. 

29.  Does  any  venous  blood    reach  the  heart  without 
coming  through  the  venm  cavce  ? 

(See  Question  28.) 

30.  What  would  you  do,  in  the  absence  of  a  surgeon,  in 
the  case  of  a  severe  wound  ? 

(See  Physiology,  pp.  128,  258.) 

31.  What  would  you  do  in  case  of  a  fever  ? 

(See  Physiology,  p.  263.) 

32.  What  is  the  most  injurious  effect  of  alcohol  upon 

the  blood  ? 

(See  Physiology,  p.  144.) 

Its  action  upon  the  red  corpuscles. 

33.  Are  our  bodies  the  same  from  day  to  day  ? 

No,  they  are  constantly  changing. 


172  ANSWERS    TO    PRACTICAL    QUESTIONS 

34.  Shoiv  hoiv  life  conies  by  death. 

(See  Physiology,  p.  122.) 

35.  Is  not  the  truth  just  stated  as  aj^plicable  to  moral 
and  intellectual  as  to  physical  life  ? 

Yes.  We  increase  our  moral  and  intellectual  strength  in 
proportion  as  we  use  those  powers. 

36.  What  vein  begins  and  ends  ivlth  capillaries  ? 

(See  Physiology,  p.  161.) 

The  portal  vein,  which  begins  with  capillaries  in  the  digestive 
organs,  and  ends  with  the  same  kind  of  vessels  in  the  liver. 

37.  Hy  what  process  is  alcohol  always  formed?    Does 
it  exist  in  nature  ? 

By  the  process  of  fermentation.  It  has  been  generally  be- 
lieved not  to  exist  in  nature,  but  recent  experiments  have  seemed 
to  indicate  that  it  does  so  exist,  though  in  extremely  minute 
quantities.  "Professor  Muntz,  of  the  National  Agronomic  In- 
stitute, in  Paris,  has,  by  refined  chemical  tests,  discovered  evi- 
dences of  alcohol  in  cultivated  soils,  in  rain  water,  in  sea  and 
river  water,  and  in  the  atmosphere.  ...  It  appears  probable 
that  the  alcohol  originates  in  the  soil,  from  the  fermentation  of 
the  organic  matters  in  it,  and  is  thence  diffused  as  vapor  in  the 
atmosphere." — W.  O.  ATWATEK,  Century  Magazine,  May,  1888. 

38.  What  percentage  of  alcohol  is  contained  in  the  dif- 
ferent kinds  of  liquor  ? 

Ale  and  porter  contain  from  six  to  eight  per  cent.  ;  wine, 
from  seven  to  seventeen  per  cent.  ;  brandy  and  whiskey,  from 
forty  to  fifty  per  cent. 

39.  Does  cider  possess  the  same  intoxicating  principle 
as  brandy? 

Yes,  because  cider  that  has  begun  to  ferment  contains  alco- 
hol, which  is  the  intoxicating  principle  in  all  spirituous  drinks. 

40.  Describe  the  general  properties  of  alcohol. 

It  is  volatile;  antiseptic,  a  solvent.  It  burns  without  smoke, 
and  with  great  heat,  and  has  a  remarkable  affinity  for  water. 
It  boils  at  172°  Fahr. 


IN   HYGIENIC    PHYSIOLOGY.  173 

41.  Shoiv  that  alcohol  is  a  narcotic  poison. 

(See  answer  to  Question  42.) 

42.  If  alcohol  is  not  a  stimulant,  how  does  it  cause  the 
heart  to  overwork  ? 

Recently,  physiological  research  has  served  to  explain  the 
reason  why,  under  alcohol,  the  heart  at  first  beats  so  quickly, 
why  the  pulses  rise,  and  why  the  minute  blood-vessels  become 
so  strongly  injected. 

At  one  time  it  was  imagined  that  alcohol  acts  immediately 
upon  the  heart,  by  stimulating  it  to  increased  motion ;  and 
from  this  idea — false  idea,  I  should  say — of  the  primary  action 
of  alcohol,  many  erroneous  conclusions  have  been  drawn.  We 
have  now  learned  that  there  exist  many  chemical  bodies  which 
act  in  the  same  manner  as  alcohol,  and  that  their  effect  is  not  to 
stimulate  the  heart,  but  to  weaken  the  contractile  force  of  the 
extreme  and  minute  vessels  which  the  heart  fills  with  blood  at 
each  of  its  strokes.  These  bodies  produce,  in  fact,  a  paralysis 
of  the  organic  nervous  supply  of  the  vessels  which  constitute 
the  minute  vascular  structures.  The  minute  vessels  when  para- 
lyzed offer  inefficient  resistance  to  the  force  of  the  heart,  and  the 
pulsating  organ  thus  liberated,  like  the  main-spring  of  a  clock 
from  which  the  resistance  has  been  removed,  quickens  in  action, 
dilating  the  feebly-resistant  vessels,  and  giving  evidence  really 
not  of  increased,  but  of  wasted  power. — B.  W.  RICHARDSON. 

43.  IVliy  is  the  skin  of  a  drunkard  always  red  and 
blotched  ? 

It  is  the  effect  of  alcoholic  action  on  the  vascular  structure. 

44.  What  danger  is  there  in  occasionally  using  alco- 
holic drinks  ? 

Aside  from  injurious  temporary  effects,  there  is  always  the 
supreme  danger  of  forming  a  habit  which  will  become  uncon- 
trollable. 

45.  Wliat    is   meant  by  a  fatty  degeneration  of  the 

heart  ? 

(See  Physiology,  p.  143.) 

In  this  disease,  fat  is  substituted  for  true  muscular  tissue. 


174  ANSWERS    TO    PRACTICAL     QUESTIONS 

46.  What  Jceeps  the  blood  in  circulation  between  the 
beats  of  the  heart  ? 

The  blood  starts  with  a  rush  from  the  heart  by  the  force 
of  its  action  ;  the  expansion  and  contraction  of  the  arteries, 
into  which  it  is  thus  powerfully  propelled,  impart  a  steady  on- 
ward pressure,  which  sends  it  to  the  capillaries  ;  there  the  proc- 
esses of  oxidation,  nutrition,  and  secretion  draw  the  current  on- 
ward, and  push  it  out  toward  the  veins  ;  thence  it  is  forced  back 
to  the  heart  by  the  power  originated  in  the  capillaries.  (See 
Draper's  Human  Physiology,  large  edition,  p.  145.) 

47.  Wliat  is  the  office  of  the  capillaries  ? 

(See  Physiology,  p.  373,  note.) 

48.  Does  alcohol  interfere  with  this  function  ? 

(See  Physiology,  p.  117,  note.) 

Alcohol  sometimes  causes  the  red  corpuscles  to  adhere  in 
masses,  which  obstruct  their  passage  through  the  tiny  capillary 
tubes. 

49.  How  does  alcohol  interfere  with  the  regular  office 
of  the  membranes  ? 

(See  Physiology,  p.  143.) 

It  absorbs  their  moisture,  and  causes  them  to  become  dry, 
hard,  and  thick. 

50.  IIoiv  does  it  chech  the  j)rocess  of  oxidation  ? 

(See  Physiology,  pp.  145,  146.) 

By  its  effect  upon  the  red  blood-corpuscles,  destroying  their 
efficiency  as  oxygen-carriers. 

!  &7—1.  How  do  clothing  and  shelter  economise  food  ? 

The  force  which  would  be  converted  into  heat  to  preserve 
the  temperature  of  the  body,  is  saved.  The  food  needed  to 
supply  this  amount  of  force  may  be  reserved  or  changed  into 
flesh,  or  into  other  forms  of  force. 

2.  Is  it  well  to  taJce  a  long  walk  before  breaJcfast  ? 

(See  Physiology,  p.  41.) 
A  vigorous  person  in  good  health   and  in  a   healthy  region 


IN   HYGIENIC    PHYSIOLOGY.  175 

may  do  so,  but  one  in  ill  health,  or  in  a  malarious  district, 
needs  to  be  braced  with  food  before  taking  any  except  very  light 
exercise. 

3.  Why  is  warm  food  easier  to  digest  than  cold  ? 

Heat  favors  the  chemical  change  whereby  the  food  is  pre- 
pared for  assimilation. 

4.  Why  is  salt  beef  less  nutritious  than  fresh  ? 

(See  Physiology,  p.  187,  note.) 

The  salts  and  juices  of  the  meat  are  extracted  by  the  brine, 

3.  What  should  be  the  food  of  a  man  recovering  from  a 
fever  ? 

It  should  be  that  which  is  nutritious,  easily  digested,  and 
not  over-stimulating.  Beef-tea  or  essence  *  is  generally  com- 
mended. As  soon  as  the  patient  will  bear  it,  beefsteak,  tender, 
broiled,  and  not  overdone,  is  most  beneficial. 

0.  Is  a  cup  of  black  coffee  a  healthful  close  to  a  hearty 
dinner  ? 

The  tannic  acid  contained  in  tea  and  coffee  is  neutralized 
by  the  milk  generally  used  with  these  beverages.  In  cafe  noir, 
black  or  clear  coffee,  the  tannic  acid  acts  unfavorably  on  the 
mucous  membrane  lining  the  stomach.  Besides,  the  coffee,  like 
a  dessert,  is  superfluous,  the  appetite  being  already  satisfied. 
It  therefore  tends,  both  actively  and  negatively,  to  delay  the 
digestion  of  the  meal.  The  glass  of  wine  sometimes  taken  to 
aid  digestion  merely  deadens  the  sensibility  of  the  stomach,  so 
that  the  food  is  hurried,  half-digested,  out  into  the  intestines,  f 

*  Dr.  Martindale  gives  the  following  recipe  for  making  this  essence : 
Cat  a  quantity  of  lean  beef  into  small  pieces,  put  it  into  a  strong  bottle, 
without  water,  cork  it  loosely,  so  that  the  steam  can  escape,  and  immerse 
tho  bottle  to  its  neck  in  a  vessel  of  cold  water.  Place  on  the  fire,  and  boil 
for  two  hours ;  then  pour  off  the  essence. 

t  Mix  some  bread  and  meat  with  gastric  juice ;  place  them  in  a  vial, 
and  keep  that  vial  in  a  sand-bath  at  the  slow  heat  of  98  degrees,  occasion- 
ally shaking  briskly  the  contents,  to  imitate  the  motion  of  the  stomach ; 
you  will  find,  after  six  or  eight  hours,  the  whole  contents  blended  into  one 


176  ANSWERS    TO    PRACTICAL     QUESTIONS 

7.  Should  iced  ivater  be  used  at  a  meal? 

Only  a  person  in  robust  health  can  endure  the  shock  of 
drinking  iced  water  at  a  meal.  Indeed,  drinking  of  iced  water 
under  any  circumstances  is  dangerous  and  hurtful.  If  used  at 
all,  it  should  be  carefully  and  slowly  sipped,  a  little  at  a  time. 

8.  Why  is  strong  tea  or  coffee  injurious  ? 

The  tannic  acid  acts  unfavorably  on  the  coatings  of  the 
stomach.*  The  nervous  system  is  over-stimulated,  and,  when 
the  reaction  occurs,  becomes  correspondingly  depressed  and 
weakened.  The  constant  decay  of  the  body,  so  essential  to  its 
highest  activity,  is  greatly  retarded.  Wakefulness  is  often  in- 
duced, and  thus  the  organs  are  deprived  of  that  rest  which  is 
absolutely  necessary  for  perfect  health. 

9.  Should  food  or  drink  be  taken  hot  ? 

The  pepsin  of  the  gastric  juice,  in  order  to  produce  its 
effect,  must  have  a  moderately  warm  temperature,  neither  too 
hot  nor  too  cold.  The  gastric  juice  will  not  act  upon  the  food 
when  near  the  freezing  point  of  water,  neither  will  it  have  any 
effect  if  raised  to  the  neighborhood  of  a  boiling  temperature. 
It  must  be  intermediate  between  the  two ;  and  its  greatest  ac- 
tivity is  about  100  degrees  Fahrenheit,  which  is  exactly  the 
temperature  of  the  interior  of  the  living  stomach. — D ALTON'S 
Physiology,  p.  103. 

10.  Are  fruit-cakes,  rich  pastry,  and  puddings  ivhole- 

some  ? 

(See  BLACK'S  Ten  Laws  of  Health,  p.  83,  et  seq.) 

They  are  too  concentrated.  They  are  not  easily  penetrated 
by  the  juices  of  the  system,  and  hence  are  not  quickly  digested. 
They  stimulate  the  appetite,  and  so  lead  to  gluttony.  They 
supply  the  system  with  an  over-abundance  of  nutrition,  for 

pultaceous  mass.  If  to  another  vial  of  food  and  gastric  juice,  treated  in 
the  same  way,  you  add  a  glass  of  pale  ale  or  a  quantity  of  alcohol,  at  the 
end  of  seven  or  eight  hours,  or  even  some  days,  the  food  is  scarcely  acted 
upon  at  all. 

*  Tea  contains  from  14  to  16  per  cent,  of  this  astringent  substance, 
and  coffee  not  over  6  per  cent.— YOUMANS. 


IN    HYGIENIC    PHYSIOLOGY.  177 

which  the  blood  has  no  use,  and  so  lead  to  biliousness  and  other 
diseases  of  the  blood  and  digestive  organs. 

11.  Why  are  warm,  biscuit  and  bread  hard  of  diges- 
tion ? 

They  form  a  pasty  mass,  which  the  juices  of  the  digestive 
organs  penetrate  very  slowly. 

12.  Should  any  stimulants  be  used  in  youth  ? 

No.  The  system  is  then  vigorous,  and  all  its  functions 
promptly  performed.  If  stimulants  are  ever  used,  it  should  be 
when  the  body  needs  forcing,  as  when  recovering  from  disease, 
or  languid  with  the  decay  of  the  natural  powers  in  old  age. 

13.  Why  should  bread  be  made  spongy  ? 

(See  Question  11.) 

14.  Which  should  remain  longer  in  the  mouth,  bread 
or  meat  ? 

Bread,  since  the  pepsin  is  essential  to  the  conversion  of 
starch  into  sugar. 

15.  Why  should  cold  ivater  be  used  in  making  soup, 
and  hot  in  boiling  meat  ? 

In  the  former  case,  we  desire  to  extract  the  juices  of  the 
meat;  in  the  latter,  to  retain  them  by  quickly  coagulating  the 
albumen  on  the  surface  of  the  meat. 

16.  Name  the  injurious  effects  of  over-eating. 

(See  Physiology,  p.  176.) 

17.  Why  do   not    buckwheat   cakes,  with   syrup   and 
butter,  taste  as  well  in  July  as  in  January  ? 

In  tne  winter,  the  system  craves  highly  carbonaceous  food ; 
in  the  summer,  it  relishes  cooling,  acid  drinks,  and  an  unstimu- 
lating  diet. 

18.  Why  is  a  late  supper  injurious  ? 

The  system  is  wearied  with  the  day's  labor,  and  the  stom- 
acn  is  unfitted  to  undertake  the  task  of  digesting  a  meal  as 


178  ANSWERS    TO    PRACTICAL     QUESTIONS 

much  as  the  body  is  to  begin  a  new  day's  task  unrefreshed  by 
sleep.* 

*  Being  allowed  for  once  to  speak,  I  would  take  the  opportunity  to 
set  forth  how  ill,  in  all  respects,  we  stomachs  are  used.  From  the  begin- 
ning to  the  end  of  life,  we  are  either  afflicted  with  too  little  or  too  much, 
or  not  the  right  thing,  or  things  which  are  horribly  disagreeable  to  us ;  or 
are  otherwise  thrown  into  a  state  of  discomfort.  I  do  not  think  it  proper 
to  take  up  a  moment  in  bewailing  the  Too  Little,  for  that  is  an  evil  which 
is  never  the  fault  of  our  masters,  but  rather  the  result  of  their  misfor- 
tunes; and,  indeed,  we  would  sometimes  feel  as  if  it  were  a  relief  from 
other  kinds  of  distress  if  we  were  put  upon  short  allowance  for  a  few 
days.  But  we  conceive  ourselves  to  have  matter  for  serious  complaint 
against  mankind  in  respect  of  the  Too  Much,  which  is  always  an  evil  vol- 
untarily incurred.  What  a  pity  that  in  the  progress  of  discovery  we  can 
not  establish  some  means  of  a  good  understanding  between  mankind  and 
their  stomachs ;  for  really  the  effects  of  their  non-acquaintance  are  most 
vexatious.  Hitman  beings  seem  to  be,  to  this  day,  completely  in  the  dark 
as  to  what  they  ought  to  take  at  any  time,  and  err  almost  as  often  from 
ignorance  as  from  depraved  appetite.  Sometimes,  for  instance,  when  we 
of  the  inner  house  are  rather  weakly,  they  will  send  us  down  an  article 
that  we  could  deal  with  when  only  in  a  state  of  robust  health.  Some- 
times, when  we  would  require  a  mild  vegetable  diet,  they  will  persist  in 
the  most  stimulating  and  irritating  of  viands. 

"What  sputtering  we  poor  stomachs  have  when  mistakes  of  that  kind 
occur  !  What  remarks  we  indulge  in  regarding  our  masters  1  "  What's  this, 
now?"  will  one  of  us  say  ;  "ah,  detestable  stuff  1  What  a  ridiculous  fellow 
that  man  is  1  Will  he  never  learn  ?  Just  the  very  thing  I  did  not  want. 
If  he  would  only  send  down  a  bowl  of  fresh  leek  soup  or  barley  broth, 
there  would  be  some  sense  in  it " ;  and  so  on.  If  we  had  only  been  allowed 
to  give  the  slightest  hint  now  and  then,  like  faithful  servants  as  we  are, 
from  how  many  miseries  might  we  have  saved  both  our  masters  and  our- 
selves ! 

I  have  been  a  stomach  for  about  forty  years,  during  all  of  which 
time  I  have  endeavored  to  do  my  duty  faithfully  and  punctually.  My  mas- 
ter, however,  is  so  reckless,  that  I  would  defy  any  stomach  of  ordinary 
ability  and  capacity  to  get  along  pleasantly  with  him.  The  fact  is,  like 
almost  all  other  men,  he,  in  his  eating  and  drinking,  considers  his  own 
pleasure  only,  and  never  once  reflects  on  the  poor  wretch  who  has  to  be 
responsible  for  the  disposal  of  every  thing  down-stairs.  Scarcely  on  any 
day  does  he  fail  to  exceed  the  strict  rule  of  temperance ;  nay,  there  is 
scarcely  a  single  meal  which  is  altogether  what  it  ought  to  be.  My  life  is 
therefore  one  of  continual  worry  and  fret ;  I  am  never  allowed  to  rest 
from  morning  till  night,  and  have  not  a  moment  in  the  four-and-twenty 
hours  that  I  can  safely  call  my  own.  My  greatest  trial  takes  place  in  the 
evening,  when  my  master  has  dined.  If  you  only  saw  what  a  mess  this 


IN   HYGIENIC    PHYSIOLOGY.  179 

19.   What  makes  a  man  "bilious"? 

(See  HALL'S  Health  by  Good  Living,  p.  Ill,  et  seq.) 

The  liver  strains  the  bile  out  of  the  blood.  This  waste  mat- 
ter is  not  withdrawn  when  the  liver  is  inactive,  and  hence  the 
face  and  eyes  become  yellow— the  color  of  bile,  and  the  func- 
tions all  become  torpid. 

said  dinner  is— soup,  fish,  flesh,  fowl,  ham,  rice,  potatoes,  table-beer,  sherry, 
tart,  pudding,  cheese,  bread,  all  mixed  up  together.  I  am  accustomed  to 
the  thing,  so  don't  feel  much  shocked ;  but  my  master  himself  would  faint 
at  the  sight.  The  slave  of  dxity  in  all  circumstances,  I  call  in.  my  friend 
Q-astric  Juice,  and  we  set  to  work  with  as  much  good-will  as  if  we  had  the 
most  agreeable  task  in  the  world  before  us.  But,  unluckily,  my  master  has 
an  impression  very  firmly  fixed  upon  him  that  our  business  is  apt  to  be 
vastly  promoted  by  an  hour  or  two's  drinking;  so  he  continues  at  table 
among  his  friends,  and  pours  down  some  bottle  and  a  half  of  wine,  per- 
haps of  various  sorts,  that  bothers  Gastric  Juice  and  me  to  a  degree  which 
no  one  can  have  any  idea  of.  In  fact,  this  wine  undoes  our  work  almost 
as  fast  as  we  do  it,  besides  blinding  and  poisoning  us  poor  servants  into 
the  bargain.  On  many  occasions  I  am  obliged  to  give  up  my  task  for  the 
time  altogether ;  for  while  this  vinous  shower  is  going  on  I  would  defy  the 
most  vigorous  stomach  in  the  world  to  make  any  advance  in  its  business 
worth  speaking  of.  Sometimes  things  go  to  a  much  greater  length  than  at 
others :  and  my  master  will  paralyze  us  in  this  manner  for  hours,  not 
always,  indeed,  with  wine,  but  occasionally  with  punch,  one  ingredient  of 
which— the  lemon— is  particularly  odious  to  us.  All  this  time  I  can  hear 
him  jollifying  away  at  a  great  rate,  drinking  health  to  his  neighbors,  and 
ruining  his  own. 

I  am  a  lover  of  early  hours,  as  are  my  brethren  generally.  To  this 
we  are  very  much  disposed  by  the  extremely  hard  work  which  we  usually 
undergo  during  the  day.  About  ten  o'clock,  having,  perhaps,  at  that  time 
got  all  our  labors  past,  and  feeling  fatigued  and  exhausted,  we  like  to  sink 
into  repose,  not  to  be  again  disturbed  till  next  morning  at  breakfast-time. 
Well,  how  it  may  be  with  others  T  can't  tell ;  but  so  it  is,  that  my  master 
never  scruples  to  rouse  me  up  from  my  first  sleep,  and  give  me  charge  of 
an  entirely  new  meal,  after  I  thought  I  was  to  be  my  own  master  for  the 
night.  This  is  a  hardship  of  the  most  grievous  kind.  Only  imagine  me, 
after  having  gathered  in  my  coal,  drawn  on  my  night-cap,  and  gone  to 
bed,  called  up  and  made  to  take  charge  of  a  quantity  of  stuff  which  I 
know  I  shall  not  be  able  to  get  off  my  hands  all  night !  Such,  O  mankind, 
are  the  woes  which  befall  our  tribe  in  consequence  of  your  occasionally 
yielding  to  the  temptations  of  "  a  little  supper."  I  see  turkey  and  tongue 
in  grief  and  terror.  Macaroni  fills  me  with  frantic  alarm.  I  behold  jelly 
and  trifle  follow  in  mute  despair.  O  that  I  had  the  power  of  standing  be- 
side my  master,  and  holding  his  unreflecting  hand,  as  he  thus  prepares  for 


180  ANSWERS    TO    PRACTICAL     QUESTIONS 

20.  WJiat  is  the  best  remedy  ? 

Diet  to  give  the  organs  rest,  and  active  exercise  to  arouse 
the  secretions  and  the  circulation. 

21.  What  is  the  practical  use  of  hunger  ? 

To  prompt  us  to  furnish  the  body  with  sufficient  food. 

22.  How  can  jugglers  drink  when  standing  on  their 
heads  ? 

Because  water  does  not  fall  into  the  stomach  by  its  own 
weight,  but  is  conveyed  thither  from  the  mouth  by  the  con- 
traction of  the  muscular  bands  of  the  oesophagus. 

23.  ^Vhy  do  tve  relish  btitter  on  bread  ? 

Butter  supplies  the  carbonaceous  element  in  which  bread  is 
lacking. 

my  torment  and  his  own  1  Here,  too,  the  old  mistaken  notion  about  the 
need  of  something  stimulating  besets  him,  and  down  comes  a  deluge  of 
hot  spirits  and  water,  that  causes  me  to  writhe  in  agony,  and  almost  sends 
G-astric  Juice  off  in  the  sulks  to  bed.  Nor  does  the  infatuated  man  rest 
here.  If  the  company  be  agreeable,  one  glass  follows  another,  while  I  am 
kept  standing,  as  it  were,  with  my  sleeves  tucked  up,  ready  to  begin,  but 
unable  to  perform  a  single  stroke  of  work. 

I  feel  that  the  strength  which  I  ought  to  have  at  my  present  time  of 
life  has  passed  from  me.  I  am  getting  weak,  and  peevish,  and  evil-disposed. 
A  comparatively  small  trouble  sits  long  and  sore  upon  me.  Bile,  from  being 
my  servant,  is  becoming  my  master ;  and  a  bad  one  he  makes,  as  all  good 
servants  ever  do.  I  see  nothing  before  me  but  a  premature  old  age  of 
pains  and  groans,  and  gripes  and  grumblings,  which  will,  of  course,  not 
last  over  long;  and  thus  I  shall  be  cut  short  in  my  career,  when  I  should 
have  been  enjoying  life's  tranquil  evening,  without  a  single  vexation  of 
any  kind  to  trouble  me.  Were  I  of  a  revengeful  temper,  it  might  be  a 
consolation  to  think  that  my  master— the  cause  of  all  my  woes— must  suffer 
ftnd  sink  with  me ;  but  I  don't  see  how  this  can  mend  my  own  case ;  and, 
from  old  acquaintance,  I  am  rather  disposed  to  feel  sorry  for  him,  as  one 
who  has  been  more  ignorant  and  imprudent  than  ill-meaning.  In  the  same 
spirit  let  me  hope  that  this  true  and  unaffected  account  of  my  case  may 
prove  a  warning  to  other  persons  how  they  use  their  stomachs  ;  for,  they 
may  depend  upon  it,  whatever  injustice  they  do  to  us,  in  their  days  of 
health  and  pride,  will  be  repaid  to  themselves  in  the  long-run— our  friend 
Madame  ISTature  being  a  remarkably  accurate  accountant,  who  makes  no 
allowance  for  ignorance  or  mistakes.— CHAMBEKS'  Memoir  of  a  /Stomach, 


IN   HYGIENIC    PHYSIOLOGY.  181 

24.  What  ivould  you  do  if  you  had  taken,  arsenic  by 

mistake  ? 

(See  Physiology,  p.  265.) 

25.  Why    should    ham    and    sausage    be   thoroughly 
cooked  ? 

The  trichina,  which  frequents  pork,  is  only  destroyed  at  a 
high  temperature. 

26.  Why  do  ive  wish  butter  on  fisJi,  eggs  with  tapioca, 
oil  on  salad,  and  milk  with  rice  ? 

To  supply  the  elements  of  food  lacking  in  the  composition 
of  fish,  tapioca,  etc. 

27.  Explain  the  relation  of  food  to  exercise. 

Their  relation  is  exceedingly  intimate.  If  we  eat  much  we 
should  take  more  exercise,  and  if,  on  the  contrary,  we  labor 
more,  we  desire  additional  food.  Violent  exercise,  directly  after 
a  hearty  meal,  is  injurious  ;  but  a  gentle,  quiet  half-hour's 
saunter  will  greatly  benefit  the  digestion. 

28.  How  do  you  explain  the  difference  in  the  manner 
of  eating  between  carnivorous  and  herbivorous  animals  ? 

Meat  requires  less  saliva  to  aid  in  its  digestion,  and  hence 
it  is  mainly  digested  in  the  stomach ;  while  vegetable  food 
needs  to  be  thoroughly  masticated  and  incorporated  with  the 

salivary  mucus. 

i 

29.  Why  is  a  child's  face  plump  and  an  old  man's 
wrinkled  ? 

In  the  child  the  processes  of  nutrition  are  more  active  than 
those  of  waste.  The  reverse  is  the  case  in  old  age. 

30.  Shoiv  how  life  depends  on  repair  and  waste. 

(See  Popular  Chemistry,  p.  19,  et  seq. ;  and  Physiology,  p.  122.) 

31.  What   is  the   difference  between  the  decay  of  the 
teeth  and  the  constant  decay  of  the  body  ? 

The  particles  of  the  teeth  lost  by  decay  are  not  renewed, 
while  in  the  body  they  are  replaced  as  fast  as  worn  out.  The 


182  ANSWERS    TO    PRACTICAL     QUESTIONS 

soundness  of  teeth  is  often  affected  by  the  general  health.  It 
has  been  said  that  a  man  who  can  preserve  his  teeth  till  he  is 
fifty  years  old  may  count  on  keeping  them  through  life. 

32.  Should  biscuit  and  cake  containing  yellow  sf>ots  of 
soda  be  eaten  ? 

Certainly  not.  The  alkali  neutralizes  the  acids  of  the  ali- 
mentary juices,  and  thus  impairs  their  functions,  while  it  cor- 
rodes and  irritates  the  delicate  mucous  lining  of  the  digestive 
organs. 

33.  Tell  hoiv  the  body  is  composed  of  organs,  how  or- 
gans are  made  up  of  tissues,  and  how  tissues  consist  of 
cells. 

(See  Physiology,  p.  175,  note.) 

34.  Why  do  we  not  need  to  drink  three  pints  of  water 

per  day  ? 

(See  Physiology,  p.  151.) 

The  amount  of  water  one  needs  depends  upon  the  charac- 
ter of  his  food,  the  nature  of  his  labor,  and  the  activity  of  the 
three  eliminating  organs — the  skin,  the  kidneys,  and  the  lungs. 
One  perspiring  freely,  or  eating  dry  food,  needs  more  drink 
than  one  whose  skin  is  inactive,  or  whose  food  consists,  in 
part,  of  soups  or  watery  vegetables. 

35.  Why,  during  a  pestilence,  are  those  who  use  liquor's 
as  a  beverage  the  first,  and  often  the  only  victims  ? 

The  nervous  system  has  become  impaired,  the  digestion  weak- 
ened, and  the  blood  impoverished ;  hence,  the  functions  of  the 
body  being  disturbed,  its  ability  to  resist  disease  is  greatly  less- 
ened. 

36.  What  two  secretions  seem  to  have  the  same  general 
use  ? 

The  saliva  and  the  pancreatic  juice  both  change  starch  into 
sugar.  They  have  other  important  uses,  however,  .in  the  pro- 
cess of  digestion.  The  former  softens  the  food  and  aids  in  the 
work  of  mastication,  while  the  latter  emulsifies  the  fats. 

37.  How  may  the  digestive  organs  be  strengthened  ? 

The   digestive  organs,   like  the   other   organs,   are  strength- 


7.V    HYGIENIC    PHYSIOLOGY.  183 

ened  by  judicious  labor.  The  stomach  is  a  muscle,  and,  like 
muscle  generally,  grows  strong  by  use  and  weak  by  disuse. 
The  same  laws  should  govern  one  in  his  daily  exercise  of  every 
organ — brain,  hand,  and  stomach. 

38.  Is  the  old  rule,  "  after  dinner  sit  awhile,"  a  good 
one? 

Yes ;  a  certain  period  of  rest,  after  a  hearty  meal,  assists 
the  process  of  digestion. 

39.  Wliat  would  you  do  if  you  had  taken  laudanum 
by  mistalw  ?    Paris  green  ?    Sugar  of  lead  ?    Oxalic  acid  ? 
Phosphorus  from  matches  ?    Ammonia  ?     Corrosive  sub- 
limate ? 

(See  Physiology,  p.  266.) 

40.  IVJiat  is  the  simplest  way  to  produce  vomiting,  so 
essential  in  case  of  accidental  poisoning  ? 

If  mustard  is  at  hand,  mix  a  little  thoroughly  with  warm 
water,  and  drink  immediately ;  if  mustard  is  not  convenient, 
warm  soap-suds  will  do ;  if  neither  is  within  reach,  the  finger 
thrust  gently  down  the  throat  may  serve  the  purpose  till  other 
means  can  be  procured,  or  medical  aid  arrives. 

41.  In  what  ^vay  does  alcohol-  interfere  with  the  diges- 
tion ? 

"  Alcohol  in  certain  quantities  will  harden  meat,  and  there- 
by interfere  with  its  digestion ;  it  will  further  precipitate  pep- 
sin and  peptones  ;  and  in  large  quantities  it  will  also  stop  the 
secretion  of  gastric  juice,  increase  the  secretion  of  mucus,  and 
even  lead  to  vomiting." 

42.  Is  alcohol  assimilated  ? 

(See  Physiology,  p.  178.) 
No. 

43.  What  is  the  effect  of  alcohol  on  the  albuminous  sub- 
stances ? 

Pure  brandy  held  in  the  mouth  a  short  time  will  cause  a 
burning  sensation,  and  the  inside  of  the  cheek  will  become 
slightly  whitened  and  corrugated.  This  effect  is  due  to  the 


184  ANSWERS    TO    PRACTICAL    QUESTIONS 

albuminous  substances  in  the  mucous  membrane  being  partly 
coagulated  by  the  alcohol,  and  it  illustrates  the  action  of  this 
agent  upon  the  tissues. 

44.  Is  there  any  nourishment  111  beer? 

The  following    table    will   show   at   a  glance  the   materials 
required  for,  and  the  result  of,  brewing : 

Materials.  Chief  Compounds  in  Beer. 

Alcohol,  or  spirits  of  wine,  from  3  to  8  per  cent. 


Malt. 
Water. 
Hops. 

Yeast  from  a  pre- 
vious brewing. 


Dextrine,  about  4.5  per  cent. 

Albuminoids,       0.5        " 

Sugar,  0.5        " 

Acetic  and  succinic  acids,  0.3  per  cent. 

Carbonic  acid,      0.15  per  cent. 

Mineral  matter,  0.3        " 


Here  it  is  seen  that  the  nutriment  of  the  malt  has  been 
converted  into  the  stimulant — alcohol.  Whatever  nourishment 
there  may  be  is  of  a  saccharine  nature,  the  dextrine  when  in 
the  stomach  becoming  converted  into  sugar.  Of  the  two  neces- 
sary nourishing  elements— the  nitrogenous  and  the  carbonaceous 
— the  former  is  practically  wanting ;  and  of  the  latter  there  is 
not  enough  to  justify  the  use  of  malt  liquor  for  the  sake  of  it. 
The  chief  difference  between  porters  or  stouts,  and  ales,  con- 
sists in  the  malt  from  which  the  former  is  made,  having  been 
more  highly  dried. — London  Medical  Temperance  Journal. 

45.  Show  how  the  excessive  use  of  alcohol  may  first  in- 
crease and  after ward  decrease  the  size  of  the  liver. 

In  the  case  of  cirrhosis  (sometimes  called  gin  -  drinker's 
liver),  the  liver  first  becomes  enlarged  from  exudation  into  the 
connective  tissue.  After  a  time,  this  becomes  organized  into 
fibrous  tissues,  and  these  fibrous  bands  contract  and  press  to- 
gether the  blood-vessels  and  cells  of  the  liver,  until  both  be- 
come atrophied  and  ultimately  destroyed.  In  this  way  the 
organ  becomes  much  smaller  in  size,  and  greatly  reduced  in 
weight. 

46.   Will  liquor  help  one  to  endure  cold  and  exposure  ? 

(See  Physiology,  p.  183.) 


IN   HYGIENIC    PHYSIOLOGY.  185 

No.  Experiments  with  Arctic  voyagers  have  abundantly 
proved  this,  while  the  certainty  that  alcohol,  in  its  secondary 
effect,  lowers  the  temperature  of  the  body,  places  the  fact  be- 
yond dispute. 

47'  What  is  a  fatty  degeneration  of  the  kidneys  ? 

v       (See  Physiology,  p.  181.) 

48.  Contrast  the  action  of  alcohol  and  water  in  the 

body. 

(See  Physiology,  p.  178,  note.) 

49.  Is  alcohol,  in  any  proper  sense  of  the  term,  a  food  ? 

This  is  a  mooted  point  between  the  defenders  and  the  op- 
posers  of  alcoholic  drinks.  The  author  of  this  Manual  consid- 
ers that  the  weight  of  argument  and  the  preponderance  of  emi- 
nent authorities  justify  a  decided  "No"  to  this  question. 

50.  Docs  liquor  strengthen  the  muscles  of  a  working- 
man  ? 

(See  Physiology,  p.  183.) 

On  the  contrary,  the  strength  of  muscle  is  directly  im- 
paired. Dr.  Parkes,  an  eminent  English  physician,  tested  this 
in  a  practical  way.  Taking  a  certain  number  of  working-men 
of  similar  age,  equal  health,  and  provided  with  the  same 
amount  of  food,  he  divided  them  into  two  gangs,  agreeing  to 
pay  them  wages  in  proportion  to  work  performed.  The  first 
gang  he  supplied  with  a  daily  ration  of  drink,  but  withheld  it 
from  the  second.  During  the  first  hour  or  two  the  "alcoholic 
gang  "  went  decidedly  ahead  of  the  other.  Then  they  began  to 
flag,  while  the  "  non-alcoholics "  went  steadily  on,  and  before 
the  day  was  done  had  far  outstripped  the  drinkers.  He  then 
reversed  the  experiment,  giving  the  second  gang  an  alcoholic 
ration,  and  withholding  it  from  the  first.  The  result  was  the 
same — the  non-drinkers  always  coming  out  ahead.  So  decided 
was  the  result  of  the  experiment,  and  so  deeply  did  it  impress 
the  men  who  were  engaged  in  it,  though  they  were  not  aware 
of  its  full  significance,  that  the  alcohol  men  begged  to  be  put 
upon  the  non-alcohol  gang,  in  order,  as  they  expressed  it,  that 
they  "  might  make  a  little  more  money." 

51.  Is  liquor  a  wholesome  "  tonic9'? 


186  ANSWERS    TO    PRACTICAL     QUESTIONS 

Certainly  not  a  "wholesome"  tonic,  nor  a  true  "tonic"  in 
any  sense,  for  the  reasons  elaborated  in  the  answers  to  the  pre- 
vious questions.  A  real  tonic  builds  up  the  system,  and  puts  it 
upon  a  permanent  basis  of  healthy  function.  The  effect  of 
alcohol  is  to  impair,  not  to  build  up. 

52.  Is  it  a  good  plan  to  talce  a  glass  of  liquor  before 
dinner  ? 

Alcohol  is  peculiarly  injurious  when  taken  upon  an  empty 
stomach,  and  furnishes  a  sorry  preparation  for  the  proper  di- 
gestion of  food. 

(See  answers  to  Questions  42,  43.) 

224—^.  Why  is  the  pain  of  incipient  hip-disease  fre- 
quently felt  in  the  knee  ? 

*Phe  sensation  of  pain  is  located  by  the  mind,  at  the  part 
of  the  body  where  the  injured  nerve  takes  its  rise. 

2.  IVIiy  does  a  child  require  more  sleep  than  an  aged 
person  ? 

The  processes  of  nutrition  are  going  on  rapidly,  and,  in 
youth,  much  rest  is  required  to  repair  the  losses  of  each  day; 
in  age,  waste  predominates,  and  the  repairs  made  are  of  a 
temporary  character.  The  building  is  soon  to  be  torn  down, 
and  little  effort  is  taken  to  beautify  or  strengthen  that  which 
is  to  be  used  for  so  short  a  time. 

3.  When  you  put  your  finger  in  the  palm  of  a  sleeping 
cJiild,  why  will  he  grasp  it  ? 

The  unconscious  action  of  the  near  nervous  centers  pro- 
duces a  contraction  of  the  muscles. 

4.  How  may  we  strengthen  the  brain  ? 

By  judicious,  habitual,  but  not  exhaustive  employment. 
The  life  of  the  brain  is  in  change.  Monotony  is  stagnation, 
and  stagnation  is  decay. 

5.  What  is  the  object  of  pain  ? 

Pain  is  monitory  in  its  character.  It  guards  against  danger 
and  warns  us  of  the  presence  of  disease,  i.e.,  the  want  of  ease. 
Were  it  not  for  this,  we  should  lose  the  use  of  the  more  deli- 


IN    HYGIENIC    PHYSIOLOGY.  187 

cate  organs.  A  child  might  gaze  at  the  sun  until  its  eyesight 
was  ruined.  The  author  knew  of  a  man  who  had  lost  the 
sense  of  feeling  in  one  leg  because  of  the  sensory  nerve  being 
severed.  He  was  constantly  bruising  and  burning  that  limb 
until  he  ruined  it  entirely. 

6*.  IVJiy  will  a  bloiv  on  the  stomach  sometimes  stop  the 
heart ? 

By  sympathy.  The  pneumogastric  or  tenth  pair  of  nerves 
supply  the  stomach  and  the  heart. 

7.  How  long  will  it  take  for  the  brain  of  a  man  six  feet 
high  to  receive  news  of  an  injury  to  his  foot,  and  to  reply? 

The  nervous  force  has  been  estimated  to  travel  at  the  rate 
of  one  hundred  feet  per  second,  although  authorities  vary  much. 
Taking  this  figure,  it  would  require  about  one  eighth  of  a 
second.* 

8.  How  can  we  grow  beautiful  ? 

If  one  is  penurious,  selfish,  or  hard-hearted,  his  face  will 
betray  the  fact  to  every  passer-by.  Purity  of  thought  and  no- 
bleness of  soul,  the  simple  habit  of  cherishing  high  and  gener- 
ous purposes,  refine  and  spiritualize  the  countenance,  making, 
at  last,  the  homeliest  features  to  glow  with  a  beauty  that  will 
be  a  true  "joy  forever." 

9.  Wliy  do  intestinal  worms  sometimes  affect  a  child's 
sight  ? 

Through  the  action  of  the  sympathetic  system  of  nerves. 

10.  Is  there    any  indication    of  character  in   physi- 
ognomy ? 

(See  Question  8 ;  also  Physiology,  p.  205.) 

11.  When  one's  finger  is  burned,  where  is  the  ache  ? 

All  pain  is  in  the  brain.  It  is  located,  however,  by  the 
mind,  at  the  place  of  the  injury. 

*  A  barefooted  boy  steps  on  a  thorn.  If  he  had  to  wait  for  news  of 
the  injury  to  be  sent  to  his  brain,  and  an  order  to  be  telegraphed  back 
to  remove  the  foot,  much  time  would  be  lost.  As  it  is,  with  the  first  prick 
the  nearer  nerve-centers  act  and  order  the  foot  off  almost  before  the  brain 
has  heard  of  the  accident. 


188  ANSWJKRS    TO    PRACTICAL    QUESTIONS 

12.  Is  a  seldom-opened  parlor  likely  to  be  a  healthy 
room  ? 

No.  It  is  generally  ill-ventilated,  and,  to  preserve  the  fur- 
niture, kept  dark,  and  hence  damp. 

13.  Why  can  an  idle  scholar  read  his  lesson  and  at  the 
same  time  count  the  marbles  in  his  pocket  ? 

(See  Physiology,  p.  204,  note.) 

The  duality  of  the  brain  may,  perhaps,  account  for  this. 

14.  In  amputating  a  limb,  what  party  ivhen  divided , 
ivill  cause  the  keenest  pain  ? 

When  a  surgical  operation  is  performed,  the  most  painful 
part  of  it  is  the  incision  through  the  skin ;  the  muscles,  carti- 
lage, and  bone  being  comparatively  without  sensation.  Hence, 
if  we  could  benumb  the  surface,  certain  of  the  lesser  operations 
might  be  undergone  without  great  inconvenience.  This  is,  in 
fact,  very  successfully  accomplished  by  means  of  the  cold  pro- 
duced by  throwing  a  spray  of  ether,  or  of  some  other  rapidly 
evaporating  liquid,  upon  the  part  to  be  cut. 

15.  What  is  the  effect  of  bad  air  on  nervous  people  ? 

The  nerves  connect  all  the  organs  of  the  body.  They  are 
therefore  especially  sensitive  to  a  derangement  in  the  function 
of  any  organ.  Bad  air  causes  impure  blood,  deranged  nutri- 
tion, and  hence  a  disturbance,  of  the  entire  economy. 

16.  Is   there  any  truth  in  the  proverb  that  "he  who 
sleeps  f  dines"  ? 

The  proverb  expresses  the  fact  that  the  nourishment  of  the 
brain  and  other  parts  goes  on  actively  during  sleep,  they  being 
controlled  by  the  sympathetic  nerves. 

17.  What  does  a  high,  wide  forehead  indicate? 

It  suggests  a  large  brain  and  a  high  intellectual  power. 

18.  How  does  indigestion  frequently  cause  a  headache? 

Through  the  action  of  the  sympathetic  system. 


IN    HYGIENIC    PHYSIOLOGY.  189 

Jf).   What  is  the  cause  of  one's  foot  being  "  asleep  "  ? 

(See  Physiology,  p.  225,  note.) 

20.  When  an  injury  to  the  nose  has  been  remedied  by 
transplanting  sltin  from  the  forehead,  why  is  a  touch  to 
the  former  felt  in  the  latter  ? 

The  mind  refers  the  sensation  to  the  place  where  the  nerve 
naturally  had  its  origin — i.e.,  the  part  over  which  its  tiny  fibers 
were  originally  distributed. 

21.  Are  closely -curtained  windoivs  healthful  ? 

No.    They  keep  out  the  sun  and  the  fresh  air. 

22.  Wrhy,  in  falling  from  a  height,  do  the  limbs  in- 
stinctively take  a  position  to  defend  the  important  organs  ? 

The  reflex  action  of  the  spinal  cord  moves  the  limbs,  into  a 
position  of  defense,  the  brain  having  no  time  to  act. 

23.  What  causes  the  pylorus  to  open  and  close  at  the 
right  time  ? 

The  reflex  action  of  the  nerves  which  preside  over  that 
organ.  In  a  similar  way,  a  tickling  in  the  throat  excites 
coughing. 

24.  VTliy  is  pleasant  exercise  most  beneficial  ? 

A  chief  condition  of  keeping  the  brain  healthy  is  to  keep 
the  unconscious  nervous  functions  in  full  vigor,  and  in  natural 
alternations  of  activity  and  repose.  Thus  it  is  that  (besides  its 
effect  in  increasing  the  breathing  and  the  general  vigor  of  the 
vital  processes)  muscular  exercise  has  so  manifest  a  beneficial 
influence  on  a  depressed  or  irritable  state  of  mind.  The  bodily 
movement,  by  affording  an  outlet  to  the  activity  of  the  spinal 
cord,  withdraws  a  source  of  irritation  from  the  brain ;  or  it 
may  relieve  excitement  of  that  organ  by  carrying  off  its  energy 
into  a  safe  channel. — HINTON. 

25.  Why  does  grief  cause  one  to  lose  his  appetite  ? 

Through  the  action  of  the  sympathetic  system. 

26.  W'Tiy  should  we  never  study  directly  after  dinner  ? 


190  ANSWERS    TO    PRACTICAL     QUESTIONS 

The  blood  then  sets  toward  the  stomach,  and  the  whole 
strength  of  the  system  is  needed  to  properly  digest  the  food. 

27.  What  produces  the    peristaltic   movement   of  the 
stomach  ? 

The  presence  of  the  food  which,  through  the  sympathetic 
system,  acting  involuntarily,  sets  in  motion  the  complicated 
apparatus  of  digestion. 

28.  Why  is  a  healthy  child  so  restless  and  full  of  mis- 
chief? 

Nature  prompts  it  to  exercise  all  the  muscles  in  its  body  in 
order  to  their  proper  development. 

29.  Why  is  a  slight  blow  on  the  bach  of  a  rabbit's  neclt 
fatal  ? 

The  medulla  oblongata  is  not  defended  with  thick  muscles 
as  in  man. 

30.  Why  can  one  walk  and  carry  on  a  conversation  at 
the  same  time  ? 

(See  Question  13.) 

31.  IVJiat  are  the  dangers  of  over-study  ? 

(See  HINTON'S  Health  and  Us  Conditions,  p.  193,  et  seq.,  and  CUTLER'S  Ana- 
lytical Anatomy,  p.  248 ;  also,  Physiology,  p.  331.) 

Exhaustive  mental  labor  overstrains  the  delicate  nerve-cells 
of  the  brain,  and  the  condition  of  the  blood-vessels  of  the  en- 
tire body,  especially  of  the  vital  organs,  is  regulated,  moment 
by  moment,  by  its  changing  moods.  Even  the  supply  furnished 
the  brain  is  subject  to  the  same  influence.  Hence  results  de- 
ranged nutrition,  impaired  circulation,  and  weakened  brain  and 
body.  Whenever  we  consume  vital  energy  faster  than  it  can 
be  replaced,  we  encroach  upon  the  capital,  and  thus  cause  an 
irreparable  injury. 

32.  What  is  the  influence  of  idleness  upon  the  brain  ? 

If  we  would  have  healthy  bodies  we  must  have  active 
brains,  that  the  streams  of  force  may  flow  into  every  organ 
from  a  full,  fresh,  energizing  source.  "The  perfect  health  of  a 
man  is  not  that  of  an  ox  or  a  horse."  The  proper  exercise  of 
the  brain  is  an  essential  element  of  real  life. 


IN    HYG1UXIC    PHYSIOLOGY.  191 

33.  State  the  close  relation  which  exists  between  phys- 
ical and  mental  health  and  disease. 

A  partial  cultivation  of  the  mental  faculties  is  incompatible 
not  only  with  the  highest  order  of  thought,  but  with  the  high- 
est degree  of  health  and  efficiency.  The  result  of  professional 
experience  fairly  warrants  the  statement  that  in  persons  of  a 
high  grade  of  intellectual  endowment  and  cultivation,  other 
things  being  equal,  the  force  of  moral  shocks  is  more  easily 
broken,  tedious  and  harassing  exercise  of  particular  powers 
more  safely  borne,  than  in  those  of  an  opposite  description, 
and  disease,  when  it  comes,  i3  more  readily  controlled  and 
cured.  The  kind  of  management  which  consists  in  awakening 
a  new  order  of  emotion,  in  exciting  new  trains  of  thought,  in 
turning  attention  to  some  new  matter  of  study  or  speculation, 
must  be  far  less  efficacious,  because  less  applicable,  in  one 
whose  mind  has  always  had  a  limited  range  than  in  one  of 
larger  resources  and  capacities.  In  endeavoring  to  restore  the 
disordered  mind  of  the  clod-hopper  who  has  scarcely  an  idea 
beyond  that  of  his  manual  employment,  the  great  difficulty  is 
to  find  some  available  point  from  which  conservative  influences 
may  be  projected.  He  dislikes  reading,  he  never  learned  amuse- 
ments, he  feels  no  interest  in  the  affairs  of  the  world ;  and, 
unless  the  circumstances  allow  of  some  kind  of  bodily  labor, 
his  mind  must  remain  in  a  state  of  solitary  isolation,  brooding 
over  its  morbid  fancies,  and  utterly  incompetent  to  initiate  any 
recuperative  movement. — Dr.  RAY. 

34.  In  ivhat  consists  the  value  of  the  power  of  habit? 
It  saves   the  "wear  and  tear"   of  our  principles.    We  can 

perform  an  act  a  few  times,  though  with  difficulty,  and  then 
ever  after  it  becomes  a  habit.  "We  resist  evil  once,  and  thence- 
forth it  is  easier  to  resist.  We  can  become  accustomed  to  do 
good,  so  that  the  chances  will  all  be  in  favor  of  our  well-being 
in  any  emergency.  By  so  much  as  the  power  of  habit  is  thus 
pregnant  with  good,  by  so  much  is  it  susceptible  of  terrible 
evil. 

35.  How  many  pairs  of  nerves  supply  the  eye  ? 

(See  Physiology,  p.  199.) 
Three ;  the  motores  oculi. 


192  AXSWEItS    TO    PRACTICAL     QUESTIONS 

86.  Describe  the  reflex  actions  in  reading  aloud. 

The  body  is  kept  erect,  the  hand  holds  the  book,  the  eyes 
are  directed  to  the  page,  the  vocal  organs  pronounce  the  words, 
the  features  express  the  sentiments,  and  the  other  hand  makes 
corresponding  gestures — yet  all  the  time  the  mind  is  intent  only 
upon  the  thought  conveyed. 

37.  Under  what  circumstances  does  paralysis  occur  ? 

When  the  nerve  leading  to  any  part  of  the  body  is  injured 
or  fails  to  keep  up  communications  between  that  portion  and 
the  mind. 

38.  If  the  eyelids  of  a  profound  sleeper  were  raised, 
and  a  candle  brought  near,  would  the  iris  contract? 

It  would,  by  reflex  action. 

39.  How  does  one  cough  in  his  sleep  ? 

By  the  reflex  action  of  the  near  nervous  centers.  A  tick- 
ling in  the  throat,  or  some  other  cause,  acts  as  the  stimulus  to 
excite  their  action. 

40.  Give  illustration  of  the  unconscious  action  of  the 
brain. 

(See  Physiology,  p.  225.  Bead  also  the  article  "  The  Antechamber  of 
Consciousness,'1  in  Popular  Science  Monthly,  March,  1888.) 

41.  Is  chewing  tobacco  more  injurious  than  smoking? 

It  is  not  only  more  filthy,  but  also  more  detrimental  to 
the  health,  as  a  chewer  is  in  danger  of  swallowing  more  of 
the  poisonous  constituents  of  tobacco,  from  the  constant  and 
profuse  excitation  of  saliva,  which  must  either  be  swallowed  or 
conspicuously  ejected.  As  a  rule,  however,  modesty  in  respect 
to  the  disposal  of  his  "tobacco  juice"  does  not  hinder  the 
veteran  chewer  from  bestowing  his  peculiar  favors  generously 
and  openly,  and  to  the  least  conscious  injury  to  himself.  On 
the  other  hand,  a  smoker,  especially  a  cigarette  smoker,  is  liable 
to  dangerous  throat  diseases,  incurred  by  the  heated  smoke  in- 
haled from  the  cigarette. 

4=2.  Ought  a  man  to  retire  from  business  ivhlle  his  fac- 
ulties are  still  unimpaired? 


IN    HYGIENIC    PHYSIOLOGY.  193 

No.  It  is  always  a  mistake  for  a  man  who  has  led  an  ac- 
tive life  to  withdraw,  at  once,  from  all  occupation  and  to  resign 
himself  to  idleness.  A  proper  degree  of  functional  exercise  is 
as  necessary  to  the  perfect  health  of  the  mind  and  the  brain  as 
to  that  of  the  body. 

43.  IVhich  is  the  more  exhaustive  to  the  braiu,  worry 
or  severe  mental  application  ? 

(See  Physiology,  p.  331.) 

Worry  is  far  more  exhaustive  of  the  vital  forces  than  the 
severest  mental  labor,  pursued  calmly  and  dispassionately. 

44.  Is  it  a  blessing  to  be  beyond  the  necessity  for  work  ? 

By  no  means.  On  the  contrary,  the  "middle-class  people," 
those  who  do  not  suffer  from  actual  bodily  want,  but  who  are 
obliged  to  work  in  order  to  procure  luxuries,  or  even  comforts, 
are  proverbially  happier  than  those  who  are  born  to  riches, 
and  who  have  no  incentive  to  systematic  exertion. 

4:5.  Shoiv  hoiv  anger,  hate,  and  the  other  degrading 
passions  are  destructive  to  the  brain. 

The  effect  of  anger  upon  the  brain  is  to  produce  first  a 
paralysis,  and,  afterward,  during  reaction,  a  congestion  of  the 
vessels  of  that  organ.  Passionate  people  often  die  suddenly  of 
faintness  in  the  moment  of  white  rage,  when  the  cerebral  ves- 
sels and  the  heart  are  paralyzed.  Or  they  may  outlive  this  first 
stage,  only  to  succumb  to  the  second,  when  reactive  congestion 
has  led  to  engorgement  of  the  vessels  of  the  brain,  and  apo- 
plexy ensues.  Intensified  hatred  acts  in  a  similar  manner,  but 
more  slowly.  The  effect  on  the  brain  of  extreme  fear  is  also 
akin  to  that  of  rage,  and  may  result  in  sudden  death  from 
syncope. 

The  more  common  and  permanent  effect  of  fear,  however, 
is  an  intense  irritability,  followed  by  doubt,  suspicion,  and  dis- 
trust, leading  toward  or  to  insanity.  From  a  sudden  terror 
deeply  felt,  the  young  mind  rarely  recovers ;  never,  I  believe, 
if  hereditary  tendency  to  insanity  be  a  part  of  its  nature. 

Of  these  three  passions,  anger  stands  first  as  most  detri- 
mental to  life.  He  is  a  man  very  rich  indeed  in  physical 


194  ANSWERS    TO    PRACTICAL     QUESTIONS 

power  who  can  afford  to  be  angry.  The  richest  can  not  afford 
it  many  times  without  insuring  the  penalty,  a  penalty  that  is 
always  severe.  What  is  still  worse  of  this  passion  is,  that  the 
very  disease  it  engenders  feeds  it,  so  that  if  the  impulse  go 
many  times  unchecked  it  becomes  the  master  of  the  man.— B.  * 
W.  RICHARDSON. 

46.  Are  not  amusements,  to  repair  the  waste  of  the 
nervous  energy,  especially  needed  by  persons  whose  life  is 
one  of  care  and  toil  ? 

Yes,  cheerful  recreation  is  necessary  in  proportion  to  the 
severity  of  toil  and  care.  ^Nothing  will  replenish  heavily-as- 
sessed brain  capital  like  occasional  rollicking  merriment. 

47.  Is   not  severe   mental  labor  incompatible  with  a 
rapidly-growing  body  ? 

Decidedly.  A  rapidly-growing  child  should  never  be  over- 
burdened with  mental  labor.  Youthful  prodigies  seldom  develop 
into  solid,  "level-headed"  adults.  Every  extra  demand  upon 
the  youthful  brain,  beyond  its  normal  power  of  healthy  endur- 
ance, is  subtracted  with  usury  from  its  future  reserve  stock. 

48.  How  shall  tve  induce  the  system  to  perform  all  its 
functions  regularly  ? 

By  uniformly  obeying  all  the  laws  of  Hygiene. 

49.  How  does  alcohol  interfere  with  the  action  of  the 

nerves  ? 

(See  Physiology,  p.  208.) 

Alcohol  has  the  same  effect  upon  the  nerve-cells  that 
water  or  ashes  has  upon  a  coal  fire.  Apply  water  in  small 
quantity,  and  your  fire  will  burn  more  slowly  ;  apply  a  large 
enough  bucketful,  and  it  will  cease  to  exist.  When  the  cook 
rakes  up  the  ashes  and  covers  her  fire  before  going  to  bed,  she 
performs  the  same  physical  experiment  as  her  master  who 
soothes  his  nerves  with  alcohol  before  retiring  at  night.  But 
the  cook  would  be  very  late  with  breakfast  if  she  trusted  to 
such  a  fire  to  cook  the  bacon,  and  the  work  accomplished  by  a 
brain  affected  by  alcohol  is  both  small  in  quantity  and  inferior 


IN    HYGIENIC    PHYSIOLOGY.  195 

in  quality.  It  is  as  difficult  to  send  proper  messages  along  a 
nerve  under  the  influence  of  alcohol,  as  it  is  to  fire  a  train  of 
damp  gunpowder. — J.  M.  HOWIE. 

50.  What  is  the  general  effect  of  alcohol  upon  the  char- 
acter ? 

(See  Physiology,  p.  212.) 

Alcohol  exalts  and  excites  the  animal  centers ;  it  lets  loose 
the  passions,  and  gives  them  more  or  less  of  unlicensed  domi- 
nation over  the  whole  man.  "  From  the  beginning  to  the  end 
of  its  influence  it  subdues  reason  and  sets  free  passion.  The 
analogies,  physical  and  mental,  are  perfect.  That  which  loosens 
the  tension  of  the  vessels  which  feed  the  body  with  due  order 
of  precision,  and  thereby  lets  loose  the  heart  to  violent  excess 
of  unbridled  motion,  loosens  also  the  reason  and  lets  loose  the 
passions.  In  both  instances,  heart  and  head  are  for  a  time  out 
of  harmony — their  balance  is  broken.  The  destructive  effects  of 
alcohol  on  the  human  mind  present  the  saddest  picture  of  its 
influence.  Memory  irretrievably  lost ;  words  and  very  elements 
of  speech  forgotten,  or  words  displaced  to  have  no  meaning  in 
them ;  rage  and  anger  persistent  and  mischievous,  or  remittent 
and  impotent ;  fear  at  every  corner  of  life ;  distrust  on  every 
side ;  grief  merged  into  blank  despair,  and  hopelessness  into 
permanent  melancholy.  As  I  have  moved  among  those  who 
are  physically  stricken  with  alcohol,  and  have  detected  under 
the  various  disguises  of  name  the  fatal  diseases,  the  pains  and 
penalties  it  imposes  on  the  body,  the  picture  has  been  suffi- 
ciently cruel.  But  even  that  picture  pales  as  I  conjure  up, 
without  any  stretch  of  imagination,  the  devastations  which  the 
same  agent  inflicts  on  the  mind." — RICHARDSON. 

51.  Does  alcohol  tend  to  produce  clearness  and  vigor  of 

thought  ? 

(See  Physiology,  p.  212.) 

Quite  the  reverse.  Its  effect  upon  the  brain  and  nervous 
system  is  strikingly  opposed  to  clearness  of  judgment  and  log- 
ical reasoning.  See  answer  to  preceding  Question. 

52.  Wliat  is  the  general  effect  of  alcohol  on  the  m  us- 
cles? 


196  A.VSWE&S    TO    PRACTICAL    QUESTIONS 

They  lose  their  nervous  control,  because  of  the  enfeebling  of 
the  nervous  stimulus.  The  muscles  of  the  lower  lip  usually 
fail  first ;  then  the  muscles  of  the  lower  limbs,  the  extensor 
muscles  giving  way  earlier  than  the  flexors.  As  they  come 
still  more  under  the  depressing  influence  of  the  paralyzing 
agent,  their  structure  becomes  temporarily  deranged,  and  their 
contractile  power  reduced. 

53.  Does  alcohol  have  any  effect  on  the  bones  ?     The 
skin  ? 

As  the  bones  are  nourished  by  tho  blood,  whatever  materi- 
ally impoverishes  the  blood  must  affect  the  bones. 

The  oft-repeated  temporary  relaxations  of  the  vessels  of  the 
skin,  resulting  from  alcoholic  potations,  ultimately  become 
chronic,  and  certain  parts,  such  as  the  nose  and  cheek,  assume 
a  distinctive  appearance  of  confirmed  vascular  relaxation.  From 
this  deficient  tonicity  of  the  skin-vessels,  the  cutaneous  secre- 
tion becomes  irregular ;  perspiration  becomes  abnormally  pro- 
fuse, and  sometimes  is  extremely  acid ;  and,  finally,  swollen 
eruptions  and  scaly  blotches  ensue. 

54.  What  is  the  cause  of  the  alcoholic  chill  ? 

(See  Physiology,  p.  210.) 

55.  Show  how  alcohol  tends  to   develop  man's  lower 
rather  than  his  higher  nature. 

(See  answer  to  Question  50.) 

56.  When  we  wisli  really  to  strengthen  the  brain,  should 
we  use  alcohol  ? 

(See  Physiology,  p.  210 ;  also,  answer  to  Question  50.) 
Never. 

57.  Wliy  is  alcohol  used  to  preserve  anatomical  speci- 
mens ? 

Because  of  its  antiseptic  properties.  These  were  well  known 
in  ancient  times,  and  palm  wine  was  used  by  the  Egyptians  in 
their  most  costly  processes  of  embalming  the  dead. 


IN  HYGIENIC    PHYSIOLOGY.  197 

58.  Wliat  is  meant  by  an  inherited  taste  for  liquor  ? 

(See  Physiology,  p.  185.) 

59.  Ought  a  person  to  be  punished  for  a  crime  com- 
mitted during  intoxication  ? 

Yes ;  because  he  knows  in  taking  the  alcoholic  poison  into 
his  system  what  the  logical  effect  will  be  upon  his  actions. 
At  the  same  time,  the  rum-seller  ought  in  justice  also  to  re- 
ceive punishment  for  the  criminal  offense  of  aiding  and  abet- 
ting such  a  state  of  moral  perversion. 

CO.  Should  a  boy  ever  smolce  ? 

Never.  Tobacco,  in  addition  to  its  other  evil  effects,  notably 
stunts  healthy  growth. 

61.  To  ivliat  extent  are  we  responsible  for  the  health  of 
our  body  ? 

To  the  extent  of  our  neglect  of  known  hygienic  rules,  or 
even,  in  this  age  of  easily-acquired  information,  to  the  extent  of 
our  lack  of  knowledge  of  these  rules. 

62.  Why  does  alcohol  tend  to  collect  in  the  brain  ? 

(See  Physiology,  p.  210.) 

One  cause  is  the  great  affinity  of  alcohol  for  water  and  the 
peculiar  moisture  which  attaches  to  the  brain. 

63.  Does  the  use  of  alcohol  tend  to  increase  crime  and 
poverty  ? 

Even  its  most  strenuous  advocates  will  not  deny  this  fact, 
of  which  both  statistics  and  common  observation  furnish  abun- 
dant proofs.  It  has  been  estimated  that  four  fifths  of  the  pau- 
perism and  crime  in  our  country  result  directly  from  strong 
drink. 

238 — 1.  Why  does  a  laundress  test  the  temperature  of 
her  flat-iron  by  holding  it  near  her  cheek  ? 

The  sense  of  warmth  is  very  keen  in  the  palms  of  the 
hand,  the  cheek,  etc.  This  sensation  is  much  less  delicate  in 
the  lips  and  the  back  of  the  hand. 


198  ANSWERS    TO    PRACTICAL     QUESTIONS 

2.  When  ive  are  cold,  why  do  ive  spread  the  palms  of 
our  hands  before  the  fire  ? 

(See  Question  1.) 

3.  What  is  meant  by  a  6i  furred  tongue  "  ? 

In  health,  the  tongue  has  hardly  a  discernible  lining,  but  in 
disease,  the  epithelium,  or  scarfskin,  accumulates,  and  gives  a 
white,  coated  appearance.  This  covering  is  likely  to  be  of  a 
yellowish  shade  when  the  liver  is  disturbed,  and  brown  or  dark 
in  blood-diseases.  One's  occupation  often  colors  it.  Thus  it  is 
said  the  tongue  of  a  tea-taster  has  a  curious  orange-tint. 

4.  IVJiy  has  sand  or  sulphur  no  taste  ? 

They  are  insoluble  in  the  saliva. 

5.  What  was  the  origin  of  the  word  palatable  ? 

The  mistaken  notion  that  the  palate,  or  roof  of  the  mouth, 
is  the  seat  of  the  taste. 

6.  Why  does  a  cold  in  the  head  injure  the  flavor  of  our 
coffee  ? 

Because  the  sense  of  taste  is  so  dependent  on  that  of  smell. 

7.  Name  some  so-called  flavors  which  are  really  sensa- 
tions of  touch. 

.     (See  Physiology,  p.  348.) 

Taste  is  not  a  simple  sense.  Certain  other  sensations,  as 
those  of  touch,  temperature,  smell,  and  pain,  are  blended  with 
it ;  and  certain  so-called  tastes  are  really  sensations  of  another 
kind.  Thus  an  astringent  taste,  like  that  of  alum,  is  more 
properly  an  astringent  feeling,  and  results  from  an  impression 
made  uj^Dn  the  nerves  of  touch,  that  ramify  in  the  tongue. 
In  like  manner,  the  qualities  known  as  smooth,  oily,  watery, 
and  mealy  tastes,  are  dependent  upon  these  same  nerves  of 
touch.  A  burning  or  pungent  taste  is  a  sensation  of  pain,  hav- 
ing its  seat  in  the  tongue  and  throat.  A  cooling  taste,  like 
that  of  mint,  pertains  to  that  modification  of  touch  called  the 
sense  of  temperature. — HUTCHISON'S  Physiology,  pp.  190,  191. 

8.  What  is  the  object  of  the  hairs  in  the  nostrils  ? 


IN    HYGIENIC    PHYSIOLOGY.  199 

They  prevent  the  entrance  of  dust  and  other  impurities. 
They  are  also  exceedingly  delicate  in  all  sensations  of  touch. 

9.  What  use  does  the  nose  subserve  in  the  process  of  res- 
piration ? 

It  warns  us  of  noxious  gases,  sifts  out  impurities,  and 
tempers  the  air  before  it  enters  the  delicate  respiratory  organs. 

10.  Why  do  we  sometimes  hold  the  nose  when  we  take 
unpleasant  medicine  ? 

(See  Question  6.) 

11.  Why  is  the  nose  placed  over'  the  mouth  ? 

As  a  sentinel  at  the  gate-way  to  the  stomach  and  the  lungs. 

12.  Describe  how  the  hand  is  adapted  to  be  the  instru- 
ment of  touch. 

Its  isolation  at  the  extremity  of  the  movable  arm,  the  mo- 
bility of  its  different  parts,  and  the  delicacy  of  the  sensation 
at  the  tips  of  the  fingers,  exquisitely  adapt  the  hand  to  be  the 
instrument  of  touch. 

13.  Besides  being  the  organ  of  taste 9  what  use  does  the 
tongue  subserve  ? 

It  aids  in  the  mastication  of  the  food  and  in  speech. 

14=.  Why  is  not  the  act  of  tasting  complete  until  we 
swalloiv  ?  * 

Because  the  organ  of  taste  is  located  especially  in  the  back 
part  of  the  tongue  and  the  soft  palate. 

15.  Why  do  all  things  have  the  same  flavor  when  one's 
tongue  is  fi  furred  "  by  fever  ? 

They  are  really  tasteless.  The  tongue  is  then  dry,  and 
there  is  no  saliva  to  dissolve  and  carry  particles  of  the  food 
into  the  cells  covering  the  nerves  of  taste. 

16.  IVJiich  sense  is  the  more  useful,  hearing  or  sight? 

(See  Wonders  of  the  Humo.n  Body,  p.  201,) 

"The  sight  speaks  more  directly  to  the  intelligence;  it  en- 
larges the  field  of  thought,  it  gives  birth  to  precise  notions  of 
light,  of  form,  of  extent ;  and  it  permits  the  communication 


200  ANSWERS    TO    PRACTICAL     QUESTIONS 

of  thought  by  conventional  signs.  Hearing  is  a  necessary  con- 
dition of  articulate  language ;  without  it  man  lives  alone,  affec- 
tion and  confidence  lose  their  most  precious  forms  of  expression, 
and  friendship  can  not  exist.  Auditory  sensations  act  upon  the 
nervous  system  with  more  force  than  visual  sensations.  We 
are  carried  away  by  rhythm,  or  it  adapts  itself  to  our  ideas 
and  our  passions  ;  music  plunges  us  into  an  ideal  world,  and 
holds  us  by  an  indefinable  charm ;  in  a  word,  if  sight  speaks 
more  especially  to  the  intellect,  hearing  addresses  itself  to  the 
affections.  Sight  is  certainly  more  necessary  to  man  than  hear- 
ing, but  still  the  blind  are  generally  gay  and  communicative, 
while  the  deaf  seem  inclined  to  melancholy.  As  to  the  relative 
influence  of  these  two  senses  on  the  development  of  the  intel- 
lect, we  know  that  the  education  of  the  deaf  is  slow,  but  may 
be  complete,  while  that  of  the  blind  is,  on  the  contrary,  rather 
rapid,  but  is  almost  always  very  limited ;  many  ideas  can  not 
be  acquired  by  them,  and,  as  has  been  remarked  by  M.  Longet, 
their  minds  rarely  attain  maturity." 

17.  Which  coat  is  the  white  of  the  eye  ? 

The  sclerotic. 

18.  IVJiat  makes  the  difference  in  the  color  of  eyes  ? 

The  varying  shade  of  the  pigment  deposited  in  the  iris  of 
the  eye. 

19.  Why  do  we  snuff  the  air  when  we  wish  to  obtain  a 
distinct  smell? 

As  muscular  actions  are  called  into  play  to  aid  the  sense  of 
taste,  as  in  smacking  the  tongue  and  lips,  so  the  act  of  "sniff- 
ing," which  is  a  mixed  respiratory  and  nasal  muscular  effort, 
is  used  to  bring  odorous  substances  more  surely  and  extensively 
into  contact  with  the  upper  and  proper  olfactory  region  of  the 
nose,  besides  causing  a  larger  amount  of  them  to  pass  over  the 
mucous  surface  in  a  given  time. — MARSHALL. 

20.  IVliy  do  red-hot  iron  and  frozen  mercury  (—40°) 
produce  the  same  sensation  ? 

The  sensation  in  both  cases  is  that  of  pain,  not  that  of 
touch. 


IN   HYGIENIC    PHYSIOLOGY.  201 

21.  Why  can  an  elderly  person  drink  tea  which  to  a 
child  would  be  unbearably  hot  ? 

The  sensation  of  touch  has  become  impaired,  and  is  much 
less  delicate. 

22.  IVJiy  does  an  old  man  hold  his  paper  so  far  from 
his  eyes  ? 

"Far  sight"  is  common  among  elderly  people,  and  is  reme- 
died by  convex  glasses.  In  old  age  the  power  of  adjusting  the 
crystalline  lens  is  lost. 

23.  Would  you  rather  be  punished  on  the  tips  of  your 
fingers  than  on  the  palm  of  your  hand  ? 

The  sense  of  touch  is  much  keener  in  the  tips  of  the  fingers 
than  in  the  palm  of  the  hand. 

24.  What  is  the  object  of  the  eyebrows  ?    Are  the  hairs 
straight  ? 

They  serve  to  prevent  the  perspiration  of  the  forehead  from 
running  down  into  the  eye.  They  act,  in  a  measure,  with  the 
eyelashes,  also  to  screen  the  eye  from  the  dust  and  glaring 
light.  The  hairs  of  the  eyebrows  overlap  each  other,  and  are 
set  obliquely  outward. 

25.  What  is  the  use  of  winking  ? 

It  serves  to  wash  the  eyeballs,  and  thus  keep  the  "windows 
of  the  soul"  clean.  The  necessity  for  winking  is  shown  by  the 
great  effort  required  to  restrain  it  even  for  a  short  time.  First 
discomfort,  then  congestion  of  the  mucous  membrane,  and  then 
a  profuse  watering  of  the  eye  follow  any  attempt  at  stop- 
ping this  necessary  act.  It  is  an  obscure  sense  of  discomfort, 
not  usually  noticed  by  the  consciousness,  that  excites  this  move- 
ment, the  objects  of  which  are  periodically  to  cleanse  the  ex- 
posed, part  of  the  eyeball,  to  moisten  and  lubricate  it  with  the 
secretions  from  the  neighboring  glands,  and  probably  in  this 
way  to  aid  in  the  preservation  of  the  polish  and  translucency 
of  the  epithelial  layer  on  the  transparent  portion  of  the  globe. 
At  the  same  time  it  carries  toward  the  inner  corner  all  for- 
eign bodies,  and  directs  the  residual  secretions  toward  the 


202  ANSWERS    TO    PRACTICAL     QUESTIONS 

lachrymal  ducts.     Finally,  it  allows  a  brief  but  periodical  rest 
to  the  levator  muscle  of  the  upper  eyelid. — MARSHALL. 

2(>.  When  you  wink,  do  the  eyelids  touch  at  once  along 
their  ivhole  length  ?  Why  ? 

In  winking,  both  lids  move,  but  the  upper  one  much  the 
more  extensively.  Moreover,  they  do  not  come  in  contact  all 
along  their  margins  at  the  same  instant  of  time,  but  meet  first 
at  the  outer  corner,  and  then  rapidly  inward  as  far  as  the 
lachrymal  papillae,  on  which  the  lachrymal  ducts  are  situated. 
By  this  sweeping  movement,  all  foreign  bodies  are  carried  to 
the  lachrymal  lake. — MARSHALL. 

27.  How  many  roivs  of  hairs  are  there  in  the  eye- 
lashes ? 

The  eyelashes,  or  cilia,  consist  of  two,  and  opposite  the 
middle  of  the  eyelid,  of  three  rows  of  finely-curved  hairs — 
those  of  the  upper  lid  being  more  numerous,  thicker,  and 
longer  than  those  of  the  lower  lid.  "Those  of  the  upper  lid 
are  curved  upward,  those  of  the  lower  lid  are  curved  down- 
ward; and  when  the  lids  are  brought  near  together,  these  two 
ranges  of  hairs  stand  like  so  many  crossed  sabers,  or  a  kind  of 
chevaux-de-frise,  guarding  the  entrance  to  the  eye." — D ALTON'S 
Physiology,  p.  330. 

28.  Do  all  nations  have  eyes  of  the  same  shape  ? 

No.  Witness  the  almond-shaped  eyes  of  the  Chinese. 
"The  greater  or  less  extent  of  the  opening  of  the  lids  makes 
the  eye  appear  larger  or  smaller;  the  conformation  of  the  pal- 
pebral  muscles  and  the  tarsal  cartilages  gives  to  the  eye  an 
elongated  and  languishing  form,  as  in  the  East,  or  round  and 
bold,  as  among  the  Occidentals ;  but  the  dimensions  and  form 
of  the  globe  are  the  same  in  all  countries  and  in  all  individu- 
als."—  Wonders  of  the  Human  Body. 

29.  IVJiy  does  snuff-taking  cause  a  floiv  of  tears  ? 

Because  of  the  action  of  the  sympathetic  system. 


IN    HYGIENIC    PHYSIOLOGY.  203 

30.  Why  does  a  fall  cause  one  to  "  see  stars  "  ?  * 

Whenever  a  nerve  is  excited  in  any  way,  it  gives  rise  to  the 
sensation  peculiar  to  the  organ  with  which  it  communicates. 
Thus,  an  electric  shock  sent  through  the  eye  gives  rise  to  the 
appearance  of  a  flash  of  light ;  •  and  pressure  on  any  part  of 
the  retina  produces  a  luminous  image,  which  lasts  as  long  as 
the  pressure,  and  is  called  a  phosphene.  If  the  point  of  the 
finger  be  pressed  upon  the  outer  side  of  the  ball  of  the  eye,  a 
luminous  image — which,  in  my  own  case,  is  dark  in  the  center, 
with  a  bright  ring  at  the  circumference  (or,  as  Newton  de- 
scribed it,  like  the  "  eye  "  in  a  peacock's  tail) — is  seen  ;  and  this 
image  lasts  as  long  as  the  pressure  is  continued. — HUXLEY. 

31.  Why  can  we  not  see  with  the  nose,  or  smell  ivith  the 

eyes  ? 

Each  set  of  nerves  is  adapted  to  transmit  to  the  brain  a 
peculiar  class  of  sensations  alone. 

32.  What  causes  the  roughness  of  a  cat's  tongue  ? 

The  sharpness  and  strength  of  the  papillae  upon  its  tongue. 
This  is  a  peculiarity  of  the  lion  tribe. 

33.  Is  the  cuticle  essential  to  touch  ? 

Yes.  If  the  cuticle  be  removed,  as  in  case  of  a  blister, 
contact  with  the  exposed  surface  produces  pain  rather  than  a 
sense  of  touch. 

34.  Can  one  ticfcle  himself? 

It  is  said  not ;  but  the  author  has  found  persons  who 
averred  that  they  could  produce  this  sensation  upon  themselves. 
The  sense,  it  is  noticeable,  is  present  only  in  those  parts  where 
that  of  touch  is  feeble. 

*  On  the  occasion  of  a  remarkable  trial  in  Germany,  it  was  claimed  by 
a  person  who  had  been  severely  assaulted  on  a  very  dark  night,  that  the 
flashes  of  light  caused  by  repeated  blows  upon  the  head  enabled  him  to 
see  with  sufficient  distinctness  to  recognize  his  assailant.  But  the  evi- 
dence of  scientific  men  entirely  refuted  this  claim,  by  pronouncing  that 
the  eye,  under  the  circumstances  named,  was  incapacitated  for  vision.— 
HUTCHISON. 


204  ANSWERS    TO    PRACTICAL     QUESTIONS 

35.  Wliy  does  a  bitter  taste  often  produce  vomiting  ? 

The  fifth  pair  of  nerves,  which  supplies  the  lip  and  sides  of 
the  tongue,  and  perceives  especially  sweet  and  sour  substances, 
ramifies  over  the  face,  and  hence  an  acid  will  "pucker"  the 
features ;  while  the  ninth  pair,  at  the  base  of  the  tongue,  which 
is  sensitive  to  salt  and  bitter  tastes,  is  distributed  also  to  the 
throat,  and  is  in  sympathy  with  the  internal  organs,  since  it 
seems  to  be  "a  common  nerve  of  feeling  for  the  mucous  mem- 
brane generally." 

36.  Is  there  any  danger  of  looking  "cross-eyed"  for 
fun  ? 

The  muscles  used  thus  in  sport  may  become  permanently 
distorted. 

37  •  Should  school-room  desks  face  a  window  ? 

No.  The  light  should  be  admitted  so  as  to  fall  over  the 
shoulder  upon  the  book.  Many  school-rooms  are  arranged  to 
accommodate  the  teacher  only,  while  a  blinding  flood  of  light 
pours  directly  into  the  faces  of  the  pupils. 

38.  Why  do  we  look  at  a  person  to  ivhom  we  are  listen- 
ing attentively? 

One  sense  instinctively  aids  another. 

39.  Do  we  really  feel  ivith  our  fingers  ? 

No.    All  sensation  is  in  the  mind. 

40.  Is  the  eye  a  perfect  sphere  ? 

No.  The  front  projects  somewhat,  while,  at  the  back,  the 
optic  nerve  is  attached  like  the  stein  to  a  fruit. 

4=1.  How  often  do  we  ivink? 

Five  or  six  times  a  minute. 

42.  Why  is  the  interior  of  a  telescope  or  microscope 
often  painted  black  ? 

To  absorb  the  scattered  rays  of  light  which  would  confuse 
the  vision.  For  the  same  reason,  the  posterior  surface  of 


IN   HYGIENIC    PHYSIOLOGY.  205 

the  iris,  the  ciliary  processes,  and  the  choroid,  are  covered  with 
a  layer  of  dark  pigment. 

43.  What  is  "  the  apple  of  the  eye  "  ? 

The  pupil. 

44.  UTiatfonn  of  (/lasses  do  old  people  require  ? 

(See  Question  22.) 

45.  Should  we  ever  ivash  our  ears  ivitli  cold  water  ? 

Rarely,  if  ever,  lest  we  chill  this  sensitive  organ. 

4(>.   What  is  the  object  of  the  winding  passages  in  the 

nose  ? 

To  furnish  additional  surface  on  which  to  expand  the  olfac- 
tory nerve. 

47 '.  Can  a  smoker  tell  in  the  darJc,  whether  or  not  his 
cigar  is  lighted  ? 

Sight  often  seems  to  be  essential  to  perfect  what  we  call  a 
sensation  of  taste. 

48.  Will  a  nerve  re-unite  after  it  has  been  cut  ? 

Nerve-fiber  seems  to  re-unite  as  readily  as  muscle-fiber. 

49.  Will  the  sight  give  us  an  idea  of  solidity  ? 

(See  Physiology,  p.  247,  note.) 

50.  Why  can  a  skillful  surgeon  determine  the  condi- 
tion of  the  brain  and  other  internal  organs  by  examining 
the  interior  of  the  eye  ? 

(See  Physiology,  p.  248,  note.) 

51.  Is  there  any  truth  in  the  idea  that  the  image  of  the 
murderer  can  be  seen  in  the  eye  of  the  dead  victim  ? 

When  the  flame  of  a  taper  is  held  near  and  a  little  on  one 
side  of  a  person's  eye,  any  one  looking  into  the  eye  from  a 
proper  point  of  view  will  see  three  images  of  the  flame,  two 
upright  and  one  inverted.  One  upright  figure  is  reflected  from 
the  front  of  the  cornea,  which  acts  as  a  convex  mirror.  The. 


206  'ANSWERS    TO    PRACTICAL     QUESTIONS. 

second  proceeds  from  the  front  of  the  crystalline  lens,  which 
has  the  same  effect ;  while  the  inverted  image  proceeds  from 
the  posterior  face  of  the  lens,  which,  being  convex  backward, 
is,  of  course,  concave  forward,  and  acts  as  a  concave  mir- 
ror.— HUXLEY.  The  images  formed  upon  the  retina  are  as 
fleeting  as  light  itself,  from  the  nature  of  the  case,  and  dis- 
appear as  soon  as  the  object  is  removed. 


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Graded  Didactics,  Vol.  II. 
History  and  Science  of  Educatipn 


Swett's  Questions  for  Written  Examinations 

Methods  of  Teaching 

White's  (E.  E.)  Elements  of  Pedagogy     .    . 


POLITICAL  ECONOMY. 

Champlln's  Lessons  in  Political  Economy 90 

Gregory's  New  Political  Economy i  20 

Jevons's  Political  Economy  (Science  Primer  Series) 3' 

L-aughlin's  Elements  of  Political  Economy i  20 

Study  of  Political  Economy 80 

PSYCHOLOGY. 

Hewett's  Psychology  for  Young  Teachers        85 

Munsell's  Psychology i  40 

Putnam's  Elementary  Psychology go 

Schuyler's  Psychology i  40 

Watts  on  the  Mind  (Fellows) 60 

SCHOOL  REGISTERS  AND   RECORDS. 

American  School  Diary,  Nos.  i  to  3 Per  doz.  72 

Brook's  School  Teacher's  Register 70 

Campbell's  Class  Record,  No,  i.     Daily  and  Weekly 72 

Class  Record,  No.  2.     Monthly 72 

School  Diary,  No.  3.     Weekly Per  doz.  48 

School  Diary,  No.  4.    Monthly Per  doz.  48 

Carter's  Record  and  Roll  Book i  oo 

Cole's  Self-Reporting  Class  Book 35 

Complete  School  Register 60 

Knight's  Scholar's  Record Per  doz.  48 

Moury's  Daily  Register  and  Grade  Book 60 

Payne's  School  Reports Per  doz.  20 

School  Record,  No.  <;,  Recitation  Book 90 

Record,  No.  6,  Roll  Book 90 

Standard  Attendance  and  Deportment  Register 60 

Teacher's  Complete  Pocket  Record 45 

Tracy's  (J.  L.)  School  Record (slated,  QOC.)  55 

Teachers'  Pocket  Record (slated,  7oc.)  45 

Scholars'  Record Per  doz.  72 

Monthly  Summaries Per  hundred  i  oo 

Weekly  and  Term  Report  Cards Per  doz.  43 

White's  New  School  Register  (for  graded  and  ungraded  schools)      .    .  60 

New  Common  School  Register  and  Term  Record 60 

New  Graded  School  Register 60 

Teacher's  Class  Record 60 

Pupil's  Daily  Record Per  doz.  96 

Monthly  School  Record 40 

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Physical   Geography. 


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APPLETONS*  PHYSICAL  GEOGRAPHY. 

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diagrams,  and  maps  in  color,  and  including  a  separate  chapter  on  the 
geological  history  and  the  physical  features  of  the  United  States. 

CORNELL'S  PHYSICAL  GEOGRAPHY. 

Large  410 $1.12 

Revised  edition,  with  such  alterations  and  additions  as  were  found  necessary 
to  bring  the  work  in  all  respects  up  to  date. 

ECLECTIC   PHYSICAL  GEOGRAPHY. 

i2mo $1.00 

By  RUSSELL  HINMAN.  A  new  work  in  a  new  and  conveniept  form.  All 
irrelevant  matter  is  omitted  and  the  pages  devoted  exclusively  to 
Physical  Geography  clearly  treated  in  the  light  of  recent  investiga- 
tions. The  numerous  charts,  cuts,  and  diagrams  are  drawn  with 
accuracy,  fully  illustrating  the  text. 

GUYOTS   PHYSICAL  GEOGRAPHY. 

Large  4to $1.60 

By  ARNOLD  GUYOT.  Revised,  with  new  plates  and  newly-engraved  maps.  A 
standard  work  by  one  of  the  ablest  of  modern  geographers.  All  parts 
of  the  subject  are  presented  in  their  true  relations  and  in  their  proper 
subordination. 

MONTEITH'S  NEW  PHYSICAL  GEOGRAPHY. 

4to       $1.00 

A  new  and  comprehensive  work,  embracing  the  results  of  recent  research  in 
this  field,  including  Physiography,  Hydrography,  Meteorology,  Ter- 
restial  Magnetism,  and  Vulcanology.  The  topical  arrangement  of 
subjects  adapts  the  work  for  use  in  grammar  grades  as  well  as  for  high 
and  normal  schools. 


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rary events  in  tables,  references  to  standard  works  for  fuller  details,  and  a  mi- 
nute index  constitute  the  "  Illustrative  Apparatus."  The  style  is  surprisingly 
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the  light  of  the  most  recent  discoveries.  The  whole  history  of  the  past  con- 
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